Start at a(0)=1. a(n) = a(n-1)+2 if n == 1,2 (mod 3) and a(n)=a(n-1)+a(n-3) if n == 0 (mod 3).

Terms

a(0) =1a(1) =3a(2) =5a(3) =6a(4) =8a(5) =10a(6) =16a(7) =18a(8) =20a(9) =36a(10) =38a(11) =40a(12) =76a(13) =78a(14) =80a(15) =156a(16) =158a(17) =160a(18) =316a(19) =318a(20) =320a(21) =636a(22) =638a(23) =640a(24) =1276a(25) =1278a(26) =1280a(27) =2556a(28) =2558a(29) =2560