a(n) = d(n)/2, where d = A026040.

Terms

a(0) =12a(1) =20a(2) =32a(3) =49a(4) =72a(5) =102a(6) =140a(7) =187a(8) =244a(9) =312a(10) =392a(11) =485a(12) =592a(13) =714a(14) =852a(15) =1007a(16) =1180a(17) =1372a(18) =1584a(19) =1817a(20) =2072a(21) =2350a(22) =2652a(23) =2979a(24) =3332a(25) =3712a(26) =4120a(27) =4557a(28) =5024a(29) =5522