Empirical: a(n) = (1/2951082477025093078506985205425766400000000)*n^39 - (1/9458597682772734225983926940467200000000)*n^38 + (1/38293917744019166906817517977600000000)*n^37 - (52891/11624791462184413045874982754713600000000)*n^36 + (3463/5208239902412371436323917004800000000)*n^35 - (22348327/276780749099628882044642446540800000000)*n^34 + (647773031/75979029164604006835784201011200000000)*n^33 - (32556163721/41443106817056731001336836915200000000)*n^32 + (27723515627/431699029344340947930592051200000000)*n^31 - (2344449895301/501327905045041100822623027200000000)*n^30 + (62396248651621/204244702055387115149957529600000000)*n^29 - (588825786343/32808637083217034988748800000000)*n^28 + (763695024283327/803140086727172564110540800000000)*n^27 - (3694889833207501/81264470313814502049054720000000)*n^26 + (25016401131306989/12747367892363059144949760000000)*n^25 - (3872232428538181617667/50709029475820249278610145280000000)*n^24 + (511899821347010105833/191567444686432052830304993280000)*n^23 - (3396356321573351385269/40563405848341061440634880000000)*n^22 + (12586343607920808934682129/5394932977829361171604439040000000)*n^21 - (1233133680230871373928900881/21579731911317444686417756160000000)*n^20 + (65367806812721760870193201/54225386290317043939737600000000)*n^19 - (5904336281059696963099827511513/281104402529003555783599718400000000)*n^18 + (22812905954245644890761855488877/84515049126367082131016908800000000)*n^17 - (13723784024975100457038466197353/10348781525677601893593907200000000)*n^16 - (1812016716171988159039645673926487/34334238707586627115725619200000000)*n^15 + (68050480955975343071807611317989027/31693143422387655799131340800000000)*n^14 - (10249811752122004199957928326094259/203161175784536255122636800000000)*n^13 + (3910951240431625868451280492396809541/4321792284871043972608819200000000)*n^12 - (958568368467796836950844574602535771/72530078854895992595865600000000)*n^11 + (39821911382448075693980652053720500691/248674556073929117471539200000000)*n^10 - (164342462570240825343621966025994693591/102096003671907258927513600000000)*n^9 + (291090415002426914142123755839082474001157/21984672790684029755724595200000000)*n^8 - (28022559068614570943727086762158577223493/324426595001413633548019200000000)*n^7 + (14115877826518948207180217681960350134151/33853209913190987848488960000000)*n^6 - (5603383931427511988820191388716526253/4651277347690518043699200000)*n^5 - (7291065554735725745084310463603118051/12359108381006233658972160000)*n^4 + (2985774756066809831374524959189973294877/112053463783746001398161280000)*n^3 - (87107916383321235748296546533354491/621897345897136204896000)*n^2 + (943604015766206248983251/2568717046665)*n - 418982256459 for n>17