a(n) = Sum_{k = 1..n} [d_3(k)*d_3(n+1-k)], where d_3 = A007425.

Terms

a(0) =0a(1) =1a(2) =6a(3) =15a(4) =30a(5) =51a(6) =72a(7) =114a(8) =128a(9) =207a(10) =204a(11) =315a(12) =294a(13) =465a(14) =402a(15) =622a(16) =510a(17) =834a(18) =636a(19) =1023a(20) =834a(21) =1251a(22) =918a(23) =1602a(24) =1074a(25) =1767a(26) =1392a(27) =2117a(28) =1428a(29) =2523