Empirical: a(n) = (1/1656632731900575744000000)*n^28 + (1/7888727294764646400000)*n^27 + (661/48834978491400192000000)*n^26 + (1783/1878268403515392000000)*n^25 + (12137423/250686222922520985600000)*n^24 + (142772789/75205866876756295680000)*n^23 + (448167044441/7553284890665523609600000)*n^22 + (24807089029/16349101494947020800000)*n^21 + (151437195067/4671171855699148800000)*n^20 + (275537977927/467117185569914880000)*n^19 + (5359163189929/573652684033228800000)*n^18 + (797577938851/6017335846502400000)*n^17 + (3714934836731407/2125889358476083200000)*n^16 + (74289229618609/3374427553136640000)*n^15 + (550385676805511/2065976052940800000)*n^14 + (3283497227409829/1032988026470400000)*n^13 + (57775723320697306019/1577544881091379200000)*n^12 + (17781188927908408957/43023951302492160000)*n^11 + (549055682513090484689977/128749174272707788800000)*n^10 + (119286883785216366942143/3065456530302566400000)*n^9 + (15460926024348082371763/52133614460928000000)*n^8 + (626569525285429348489/368621516390400000)*n^7 + (1318850890622160435326629/204008970477312000000)*n^6 + (20291412297289870359779/2615499621504000000)*n^5 - (16430571002334302055257/396684109261440000)*n^4 - (71518507150798421221/539706271104000)*n^3 + (22767422480341098379/49473074851200)*n^2 + (623416468300079/6692786100)*n - 757320 for n>5