Part 12

sum(1/binomial(2*n,n),n=1..infinity) to 1024 digits.

0.7363998587187150779097951683649234960631258329094979056821966523 0847181802807864081869444182490225974582720321801478346017690055 4229868477732944895880680415915142979334394163998909738083425408 1520029546146727664979554751571056972458855740951911198864857982 9433328581834861487045790649324680582119729407417116198674601654 4485479889543142786974292724928598532747380156659130512545236749 4154597773449101860414448973793322220865507304585980050655111918 9338017331890327068185957293937796352569292021414362805981608876 3091647656764089200563681690417652792652154091682197250552326447 7646813159383043809989583900078755611335395490521438524130346215 3457599854790211802421898533425927038158436578567901788663851909 9589847649578146455045212664074436825052408587935995452420291968 6774100311819740383505356065846433687090253752952485814436801506 6642240052190351749758439051568244234310796570611672868391753708 6438175031998334537917178650178729583132166807457526236785528510 1696922360975795282761033968077326069723073543573616136752770598

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sum(1/(n*binomial(2*n,n)),,n=1..infinity); to 1024 digits.

0.6045997880780726168646927525473852440946887493642468585232949784 6270772704211796122804166273735338961874080482702217519026535083 1344802716599417343821020623872714469001591245998364607125138112 2280044319220091497469332127356585458688283611427866798297286974 4149992872752292230568685973987020873179594111125674298011902481 6728219834314714180461439087392897799121070234988695768817855124 1231896660173652790621673460689983331298260956878970075982667878 4007025997835490602278935940906694528853938032121544208972413314 4637471485146133800845522535626479188978231137523295875828489671 6470219739074565714984375850118133417003093235782157786195519323 0186399782185317703632847800138890557237654867851852682995777864 9384771474367219682567818996111655237578612881903993178630437953 0161150467729610575258034098769650530635380629428728721655202259 9963360078285527624637658577352366351466194855917509302587630562 9657262547997501806875767975268094374698250211186289355178292765 2545383541463692924141550952115989104584610315360424205129155898

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sum(1/n^n,n=1..infinity); to 1024 places.

1.291285997062663540407282590595600541498619368274522317310002445 1369445387652344555588170411294297089849950709248154305484104874 1928486419757916355594791369649697415687802079972917794827300902 5649230550720966638128467012053685745978703001277894129288253551 7702223833753193457492599677796483008495491110669649755010519757 4291162109702156166953289768924278900580939081478809403679930558 9535200633716110465094638606808864998606531021853412479159737305 2710686824652246770336860469870234201965831431339687388172956893 5536851798521420666264165438061224569940966356043885239969381304 4840101532338556989547899226146597068180753342912289091004995136 4103584723741679660994037428872280908239472403012423375069665874 3147683502983470096596930198071220594154742391888495488920431478 4037389693592832744937301860181757952468190913559650620576842700 8907326547137233834847185623248044173423385652705113744822086069 8381169706447896315548031108686846807807010570342300009547766282 9927022264266182213029160934485049255679995121281765081062180734

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The Traveling Salesman Constant, conjectured to be is equal to 4/153*(1+2*sqrt(2))*sqrt(51) to 1000 digits.

.71478270079129427201898487962108409673134559709443031939645700411546117738335\ 879706770213413096294533561547227555717895434127457058654186783324525211448435\ 423370160734747472156550615029635220251467885538763575736849440141040232425552\ 364704664879061099570515393895856312208463669793487083110116620844381148478166\ 953397235099760820248716126335472464734965931893615249427223312525010786175723\ 903850094286618856777573472030439593602004416562703436281430743460123517870481\ 605658651710683396096658326275655282564938079930443149087689479702230621110332\ 425071472991466740480185001283536160284031917506648494911514005453049419741227\ 682161417117934301981301137112382110439175900888848785626934265741110708345544\ 731999904108101036079296059394893034776038533840976912765053467151339515952296\ 425034733122079333744376059531233173573812633038639781766805813536012423214277\ 007401299039458343003042376467569131088941308597225474822014342730622766746260\ 22472480156659330677754354367566446245619515011589704068286465445

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The Tribonacci constant, is such that 1/(1-x-x^2-x^3) once expanded into a series will give coefficients proportional to approx. c**n and c = (to 1000 digits).

1.8392867552141611325518525646532866004241787460975922467787586394042032220819\ 664257384354194283070141419798268592409741641784507465074369438315458204995137\ 962496555396446136661215402779726781189410412116092232821559560718167121823659\ 866522733785378156969892521173957914132287210618789840852549569311453491349853\ 459576175035965221323814247272722417358187700069790551025490449657107425265477\ 228110065989375556363093330528262357538519719942991453008254663977472900587005\ 974481391931672825848839626332970700687236831127837750250557122275153259578946\ 560570686422283918659698294691356239220443192476147068811451726766712743964146\ 212571843342662340390218352494591033227231061513286997030808036302223324997105\ 243107472354231399744381826565607351940357874911762680524537079221110849710806\ 876410050156541475662235008885665949715821834184868714802901255436993480513679\ 165025853053878276666126224317766358200942985505387325991651787730184472388604\ 26222324857820792721049160181783725613203439814302274533997621231

/ 19 1/2\1/3 4 |---- + 1/9 33 | + ----------------------- + 1/3 \ 27 / / 19 1/2\1/3 9 |---- + 1/9 33 | \ 27 /

in fact the n'th Tribonacci number is given by this EXACT formula. ---------------------------------------------------------------------

See : http://www.labri.u-bordeaux.fr/~loeb/book/92pl.html

Comment calculer le nieme nombre de Tribonacci

Resume of a conference given in 1993 (Universite Bordeaux I, LaBRI).

1/2 1/3 1/2 1/3 n 1/2 1/3 (1/3 (19 + 3 33 ) + 1/3 (19 - 3 33 ) + 1/3) (586 + 102 33 ) 3 --------------------------------------------------------------------------- 1/2 2/3 1/2 1/3 (586 + 102 33 ) + 4 - 2 (586 + 102 33 )

To get the actual n'th Tribonacci number just round the result to the nearest integer.

Here is the formula 'lprinted'...

3*(1/3*(19+3*33^(1/2))^(1/3)+1/3*(19-3*33^(1/2))^(1/3)+1/3)^n/((586+102*33^(1 /2))^(2/3)+4-2*(586+102*33^(1/2))^(1/3))*(586+102*33^(1/2))^(1/3);

This formula has 2 parts, first the numerator is the root of (x^3-x^2-x-1) no surprise here, but the denominator was obtained using LLL (Pari-Gp) algorithm. The thing is, if you try to get a closed formula by doing the Z-transform or anything classical, it won't work very well since the actual symbolic expression will be huge and won't simplify.

The numerical values of Tribonacci numbers are c**n essentially and the c here is one of the roots of (x^3-x^2-x-1), then there is another constant c2. So the exact formula is c**n/c2.

Another way of doing 'exact formulas' are given by using [ ] function the n'th term of the series expansion of 1/(1+x+x**2) is

1 - 2 floor(1/3 n + 2/3) + floor(1/3 n + 1/3) + floor(1/3 n)

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