a(n) = A030068(4n+3).

Terms

a(0) =2a(1) =5a(2) =9a(3) =16a(4) =23a(5) =35a(6) =48a(7) =69a(8) =87a(9) =116a(10) =145a(11) =189a(12) =228a(13) =287a(14) =345a(15) =430a(16) =501a(17) =605a(18) =704a(19) =843a(20) =965a(21) =1136a(22) =1299a(23) =1523a(24) =1716a(25) =1981a(26) =2231a(27) =2566a(28) =2863a(29) =3261