Empirical: a(n) = (1/1311592212011152479336437869078118400000000)*n^39 + (1/8407642384686874867541268391526400000000)*n^38 + (1/121027690647764280594386229657600000000)*n^37 + (4453/4133259186554457971866660535009280000000)*n^36 + (36623/574063775910341384981480629862400000000)*n^35 + (2286883/984109330132013802825395365478400000000)*n^34 + (59427001/202610744438944018228757869363200000000)*n^33 + (3662363/920957929267927355585263042560000000)*n^32 + (698407621/2302394823169818388963157606400000000)*n^31 + (2071871299/68557662228381689001384345600000000)*n^30 - (88375072061/112686732168489442841355878400000000)*n^29 + (55259357819/919891691171342390541680640000000)*n^28 - (26908476069689/48830917273012091897920880640000000)*n^27 - (64255416499361/15024897622465259045514117120000000)*n^26 + (1211660755628293/577880677787125347904389120000000)*n^25 - (428497699693404821/4507469286739577713654235136000000)*n^24 + (18168644312007664819/3990988430967334433964687360000000)*n^23 - (13599662603639123677/72112721508161887005573120000000)*n^22 + (44259928059820224087949/6393994640390353981160816640000000)*n^21 - (1430292603085062198472427/7672793568468424777392979968000000)*n^20 + (83424978564143896333018147/27763397780642326497145651200000000)*n^19 + (626347078074282429025126279/76883255392547981069018726400000000)*n^18 - (162932546987425141092549050651/75124488112326295227570585600000000)*n^17 + (242180456724635530056260696071/3219620919099698366895882240000000)*n^16 - (313750645679320685071247484926723/183115939773795344617203302400000000)*n^15 + (468085529688808797260462819635799/14085841521061180355169484800000000)*n^14 - (361252209405486577647260841889039/541763135425430013660364800000000)*n^13 + (246775977580464637556296713305489/17461787009579975646904320000000)*n^12 - (640425220695650312257449459590478503/2320962523356671763067699200000000)*n^11 + (2976965893392670811240941519946738587/663132149530477646590771200000000)*n^10 - (15691414208286516538847211891059291149649/263816073488208357068695142400000000)*n^9 + (1926690096810214572543957878204302137389/2931289705424537300763279360000000)*n^8 - (3289587300132723694936174544088626486101/519082552002261813676830720000000)*n^7 + (729499652952356617189425555198998628947/13309809025699020863508480000000)*n^6 - (1191606382911729702405983954170131320027/2883791955568121187093504000000)*n^5 + (20718070606600149135698330007153758117/8239405587337489105981440000)*n^4 - (505597319455365651210352032811940902871/44821385513498400559264512000)*n^3 + (4680890022338628214491295905910493/138199410199363601088000)*n^2 - (647104987407124247146843/10837589162400)*n + 46943720707 for n>19