Empirical: a(n) = (1/1010247037153000705636579512318796796754678251520000000000)*n^47 - (1/2686827226470746557544094447656374459453931520000000000)*n^46 + (1/7026681206853864812145392475073878939402240000000000)*n^45 - (127/3664896472594368705942498820332650584080384000000000)*n^44 + (72329/9439884853652161818336739385705312110510080000000000)*n^43 - (81539/59872419790605677494736190607010436218880000000000)*n^42 + (429055931/1975789853089987357326294290031344395223040000000000)*n^41 - (16964821/566941134315634822762207830712007000064000000000)*n^40 + (1827234659/491734657314581223824363934801230561280000000000)*n^39 - (507972146243/1235640933764845126533017066936425512960000000000)*n^38 + (1640156111807/39742837050916071321237391041814855680000000000)*n^37 - (90602840371/24167941449881394722374089147049574400000000)*n^36 + (6896619141543191/22177640389302926921707987687880785920000000000)*n^35 - (386228642185150949/16392168983397815550827643073651015680000000000)*n^34 + (472091170064351179/288021303757180869113090749193256960000000000)*n^33 - (426965885290472681/4073028537980335522811384332025856000000000)*n^32 + (47100747825947143625251/7616563366023227427657288700888350720000000000)*n^31 - (41401107169380409667033/122847796226181087542859495175618560000000000)*n^30 + (714437425832081190815995163/42013946309353931939657947350061547520000000000)*n^29 - (589442711942561863039637/741052055901824357344703189876736000000000)*n^28 + (4138300597776596584700524127/119821988437358893268404827806760960000000000)*n^27 - (569185815975965973657984885269/408623704158172636017893387135877120000000000)*n^26 + (163544534518752339012529560528817/3132781731879323542803849301375057920000000000)*n^25 - (200994974625869228586313218455477/110568767007505536804841740048531456000000000)*n^24 + (21290867886418332771208338997711489/362189192322016654652223684052254720000000000)*n^23 - (232276730736190008644249112631866701/131705160844369692600808612382638080000000000)*n^22 + (79265259917337030447380680303974383/1616916037151860065411712875233280000000000)*n^21 - (60857585913006825102371224281427606751/48291892309602220620296491206967296000000000)*n^20 + (2250002445476983293023101885534802801/75274384942512921288516847534080000000000)*n^19 - (15024586569408678096426533515266502089541/23033961792408953914286155345428480000000000)*n^18 + (1064011077877873794147065038577437650966911/81535442607731348976867601793679360000000000)*n^17 - (26425325228994326799914489489167889830135313/110888201946514634608539938439403929600000000)*n^16 + (831175224890362291169424698077063846965271259/210390561728878212984953008199761920000000000)*n^15 - (247729484242257766360628691978964700287651283/4195823168382186583745501588029440000000000)*n^14 + (112736477575864215276229064569328805498044789/143039426194847269900414826864640000000000)*n^13 - (27426320212410665458099601016474314382917/2956199874857986926046445568000000000)*n^12 + (13720116479138178578504440093160196340240816328873/145248590666078799957765678079549440000000000)*n^11 - (1443427524169251064911674070485645151658026586043/1793192477358997530342786149130240000000000)*n^10 + (325130524317293549697070523931430545850702704281/60671925925680367567989005045760000000000)*n^9 - (157215426146907042983743454699228680841534721719/7032127362192147177814847643648000000000)*n^8 - (57730612875783149128815834452990004774547179474761/2021824518222269715461491383144345600000000)*n^7 + (1531260273681289171755604278348670505406567629149/976726820397231746599754291374080000000)*n^6 - (11492431235654045096559324539290390817365777925329/689987732409187283847969281549260800000)*n^5 + (1237685571728360417241018342162175103490344421103/10952186228717258473777290183321600000)*n^4 - (12040107032687443295289959544247851472622437/22272823053760375542617851680000)*n^3 + (4107286385195229860769185766558085320773/2292483225343906906575264000)*n^2 - (413702984217720271054500548227873/110680160865928453800)*n + 3725941823309 for n>18