Empirical: a(n) = (1/48569119454267387884339200000000)*n^36 - (1/2698284414125965993574400000000)*n^35 + (56039/562245378063447714032517120000000)*n^34 - (61/123096962903874704769024000000)*n^33 + (1829837101/9967077156579300385121894400000000)*n^32 + (150746251/88991760326600896295731200000000)*n^31 + (10580586529/47609487658598395139850240000000)*n^30 + (2249206760813/495138671649423309454442496000000)*n^29 + (32012453785633/121955337844685544200601600000000)*n^28 + (52634065124899/8711095560334681728614400000000)*n^27 + (1214453073075629/4065177928156184806686720000000)*n^26 + (111831672183383/17868913969917295853568000000)*n^25 + (17111309251557457/57603735824075493212160000000)*n^24 + (1207262888909617769/273617745164358592757760000000)*n^23 + (63231985786126291/339897820079948562432000000)*n^22 - (86445241026899/371726939253532262400000)*n^21 - (87876522550276029478537/706987465766293009858560000000)*n^20 + (503809776187216500630259/50499104697592357847040000000)*n^19 - (31609375740380419776182081/114205667546862716977152000000)*n^18 + (549289683889903860984161563/197956490414562042760396800000)*n^17 + (25999109475101917344567154249/252495523487961789235200000000)*n^16 - (183839932161536911455240517579/31561940435995223654400000000)*n^15 + (62801804620965997550265491130919/381110430764642325626880000000)*n^14 - (11136495922434982856054198314189/3350421369359492972544000000)*n^13 + (107142955669356159162514738295647697/2052133088732689445683200000000)*n^12 - (15387633425414260346870327149746097/23319694190144198246400000000)*n^11 + (3824082203988204294383653300992577/563772826574914682880000000)*n^10 - (23662881087777948964222238402502829/418802671169936621568000000)*n^9 + (191489517633708564949130709584631119209/511676041304380900147200000000)*n^8 - (17215255296356818171677008774493640837/9137072166149658931200000000)*n^7 + (153649585502169529967943865110564013/24013309492337679360000000)*n^6 - (1030241660158529999086055047133509207/132942649620510842112000000)*n^5 - (42913743054084908115334843388601407/734349874094250365952000)*n^4 + (1461514303698652141809448030781879/3450892265480499840000)*n^3 - (6050441534344184037675151595489/4336438693394808000)*n^2 + (6908059837966372407659503/2776991401800)*n - 1914821814227 for n>15