a(n) = a(n-1) + a(n-1-(number of odd terms so far)).

Terms

a(0) =1a(1) =2a(2) =3a(3) =4a(4) =6a(5) =9a(6) =12a(7) =16a(8) =22a(9) =31a(10) =40a(11) =52a(12) =68a(13) =90a(14) =121a(15) =152a(16) =192a(17) =244a(18) =312a(19) =402a(20) =523a(21) =644a(22) =796a(23) =988a(24) =1232a(25) =1544a(26) =1946a(27) =2469a(28) =2992a(29) =3636