Empirical: a(n) = (1/8222838654177922817725562880000000)*n^31 + (1/16578303738261941164769280000000)*n^30 + (67/5305057196243821172726169600000)*n^29 + (41/26133286681004045185843200000)*n^28 + (383/2688609740844037570560000000)*n^27 + (108503/10370351857541287772160000000)*n^26 + (14350591/23452949585516450807808000000)*n^25 + (27283621/938117983420658032312320000)*n^24 + (746864683/617182883829380284416000000)*n^23 + (6086132449/145670494319977955328000000)*n^22 + (11459863603/9711366287998530355200000)*n^21 + (9079260647/277467608228529438720000)*n^20 + (9295334338692973/13256014983117993934848000000)*n^19 + (7406621998640167/697684999111473364992000000)*n^18 + (40885271501316793/139536999822294672998400000)*n^17 + (119603307396917/46903193217578041344000)*n^16 - (1131346399375370033/66446190391568891904000000)*n^15 + (10485173561922681833/4746156456540635136000000)*n^14 - (5463952009750785885511/305908038071953706188800000)*n^13 - (9164410096052944963129/30590803807195370618880000)*n^12 + (29362199862206291323251859/1911925237949710663680000000)*n^11 - (29562579123647095917221749/136566088424979333120000000)*n^10 + (3101899210986712657125907/6980044519498943692800000)*n^9 + (5406431224932283020107753/166191536178546278400000)*n^8 - (39154279893916528092647944621/73516672601204152320000000)*n^7 + (62619875092550151222599787781/18379168150301038080000000)*n^6 + (16192690712390399507478803/8061038662412736000000)*n^5 - (20614836186524341006051559/109399810418458560000)*n^4 + (1904697969423497571208793/1438818368315328000)*n^3 - (558516960677532721524481/139885119141768000)*n^2 + (46127701417206897941/12033629407800)*n + 2967221 for n>13