Doubly pentagonal pyramidal numbers.

Terms

a(0) =0a(1) =1a(2) =126a(3) =3078a(4) =32800a(5) =213750a(6) =1008126a(7) =3783976a(8) =11985408a(9) =33297075a(10) =83338750a(11) =191592126a(12) =410450976a(13) =828497488a(14) =1589341950a(15) =2917620000a(16) =5154021376a(17) =8801526501a(18) =14585352318a(19) =23529456550a(20) =37052820000a(21) =57089119626a(22) =86233820926a(23) =127923156648a(24) =186649920000a(25) =268221484375a(26) =380065968126