a(1)=1, a(n) = a(n-1) + sum of odd numbers which are among the first (n-1) terms of the sequence.

Terms

a(0) =1a(1) =2a(2) =3a(3) =7a(4) =18a(5) =29a(6) =69a(7) =178a(8) =287a(9) =683a(10) =1762a(11) =2841a(12) =6761a(13) =17442a(14) =28123a(15) =66927a(16) =172658a(17) =278389a(18) =662509a(19) =1709138a(20) =2755767a(21) =6558163a(22) =16918722a(23) =27279281a(24) =64919121a(25) =167478082a(26) =270037043a(27) =642633047a(28) =1657862098a(29) =2673091149