Doubly heptagonal pyramidal numbers.

Terms

a(0) =0a(1) =1a(2) =456a(3) =14976a(4) =181780a(5) =1273970a(6) =6293756a(7) =24395756a(8) =79119496a(9) =223821235a(10) =568280240a(11) =1321714636a(12) =2858876956a(13) =5817509516a(14) =11237224740a(15) =20751835560a(16) =36849296016a(17) =63215722181a(18) =105182448536a(19) =170297734920a(20) =269047574180a(21) =415753060646a(22) =629674964556a(23) =936359517556