a(n) = (n+1)*(5*n^2+4*n+1).

Terms

a(0) =1a(1) =20a(2) =87a(3) =232a(4) =485a(5) =876a(6) =1435a(7) =2192a(8) =3177a(9) =4420a(10) =5951a(11) =7800a(12) =9997a(13) =12572a(14) =15555a(15) =18976a(16) =22865a(17) =27252a(18) =32167a(19) =37640a(20) =43701a(21) =50380a(22) =57707a(23) =65712a(24) =74425a(25) =83876a(26) =94095a(27) =105112a(28) =116957a(29) =129660