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

Terms

a(0) =1a(1) =2a(2) =3a(3) =5a(4) =8a(5) =11a(6) =16a(7) =21a(8) =29a(9) =40a(10) =51a(11) =67a(12) =88a(13) =109a(14) =138a(15) =167a(16) =207a(17) =258a(18) =309a(19) =376a(20) =443a(21) =531a(22) =640a(23) =749a(24) =887a(25) =1054a(26) =1221a(27) =1428a(28) =1635a(29) =1893