a(n) = n^4 if n odd, 15*n^4/16 if n even.

Terms

a(0) =0a(1) =1a(2) =15a(3) =81a(4) =240a(5) =625a(6) =1215a(7) =2401a(8) =3840a(9) =6561a(10) =9375a(11) =14641a(12) =19440a(13) =28561a(14) =36015a(15) =50625a(16) =61440a(17) =83521a(18) =98415a(19) =130321a(20) =150000a(21) =194481a(22) =219615a(23) =279841a(24) =311040a(25) =390625a(26) =428415a(27) =531441a(28) =576240a(29) =707281