Empirical: a(n) = (1/1311592212011152479336437869078118400000000)*n^39 + (1/6114649007044999903666377012019200000000)*n^38 + (47/3267747647489635576048428200755200000000)*n^37 + (71/46756325639756311898944123699200000000)*n^36 + (383/3069859764226424518617543475200000000)*n^35 + (35449/6834092570361206964065245593600000000)*n^34 + (43669033/101305372219472009114378934681600000000)*n^33 + (67531/3405909501730500575389286400000000)*n^32 + (7488127/25582164701886870988479528960000000)*n^31 + (402335873/6962887570070015289203097600000000)*n^30 + (1261029121301/3267915232886193842399320473600000000)*n^29 - (149006233/487821351378742176802406400000000)*n^28 + (1108133000866459/244154586365060459489604403200000000)*n^27 - (236146127431793/1878112202808157380689264640000000)*n^26 + (58708858751/21460215307008517079040000000)*n^25 + (7839611067588067/66678539744668309373583360000000)*n^24 - (216779406667492912849/31927907447738675471717498880000000)*n^23 + (343949747168197/2129857685278571888640000000)*n^22 + (29902632796399941365807/19181983921171061943482449920000000)*n^21 - (16943660118255319081889/86796307335615664902635520000000)*n^20 + (7890850911442993301218261/1633141045920136852773273600000000)*n^19 + (82466912750697306326221417/2839438409383874300844441600000000)*n^18 - (210394977308444823960127786093/37562244056163147613785292800000000)*n^17 + (24664466683454767981509059099/127762734884908665353011200000000)*n^16 - (30005152196751863494841724192223/8323451807899788391691059200000000)*n^15 + (108203956571582287863803329609567/3521460380265295088792371200000000)*n^14 + (998407966388456972317594886323/3344216885342160578150400000000)*n^13 - (538500951242710361199958374395429/36938395597188410022297600000000)*n^12 + (15599176782953491379129512118361283/58024063083916794076692480000000)*n^11 - (102416634799941472116864154941439769/27630506230436568607948800000000)*n^10 + (393191714281306639917272291344637022569/7759296279064951678491033600000000)*n^9 - (12282937894883249591726172771727965953/17082107840469331589529600000000)*n^8 + (22934769418169761165428530735955121752443/2595412760011309068384153600000000)*n^7 - (7007476584643415975211634435842442077907/86513758667043635612805120000000)*n^6 + (22454283561513245895803463642515218301/43693817508607896774144000000)*n^5 - (9247558858319650634419116795712253/4251499271071975802880000)*n^4 + (43851281129625383418881721980546181193/6591380222573294199891840000)*n^3 - (355637046190159485592538088973201/15946085792234261664000)*n^2 + (56141905322129375758148999/667866432132900)*n - 160171565370 for n>20