a(n) is the number of terms in the expansion of (x-y)*(x^4-y^4)*(x^9-y^9)*...*(x^(n^2)-y^(n^2)).

Terms

a(0) =2a(1) =4a(2) =8a(3) =16a(4) =24a(5) =40a(6) =68a(7) =103a(8) =162a(9) =236a(10) =344a(11) =453a(12) =612a(13) =790a(14) =994a(15) =1229a(16) =1432a(17) =1782a(18) =2134a(19) =2517a(20) =2968a(21) =3460a(22) =3974a(23) =4543a(24) =5160a(25) =5822a(26) =6546a(27) =7347a(28) =8184a(29) =9080