a(1)=1, a(n)=a(n-1)+n^1 if n odd, a(n)=a(n-1)+ n^5 if n is even.

Terms

a(0) =1a(1) =33a(2) =36a(3) =1060a(4) =1065a(5) =8841a(6) =8848a(7) =41616a(8) =41625a(9) =141625a(10) =141636a(11) =390468a(12) =390481a(13) =928305a(14) =928320a(15) =1976896a(16) =1976913a(17) =3866481a(18) =3866500a(19) =7066500a(20) =7066521a(21) =12220153a(22) =12220176a(23) =20182800a(24) =20182825a(25) =32064201a(26) =32064228a(27) =49274596a(28) =49274625