a(n) = A030068(4n+1).

Terms

a(0) =1a(1) =3a(2) =6a(3) =11a(4) =17a(5) =26a(6) =37a(7) =53a(8) =70a(9) =93a(10) =119a(11) =154a(12) =191a(13) =239a(14) =292a(15) =361a(16) =431a(17) =518a(18) =611a(19) =727a(20) =846a(21) =991a(22) =1145a(23) =1334a(24) =1525a(25) =1753a(26) =1992a(27) =2279a(28) =2571a(29) =2916