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

Terms

a(0) =1a(1) =121a(2) =1563a(3) =8403a(4) =29525a(5) =80525a(6) =185647a(7) =379687a(8) =709929a(9) =1238049a(10) =2042051a(11) =3218171a(12) =4882813a(13) =7174453a(14) =10255575a(15) =14314575a(16) =19567697a(17) =26260937a(18) =34671979a(19) =45112099a(20) =57928101a(21) =73504221a(22) =92264063a(23) =114672503a(24) =141237625a(25) =172512625