a(0) = a(1) = a(2) = 1, for n > 2, a(n) = a(n-1) + a(n-k) + k with k = 2.

Terms

a(0) =1a(1) =1a(2) =1a(3) =4a(4) =7a(5) =10a(6) =16a(7) =25a(8) =37a(9) =55a(10) =82a(11) =121a(12) =178a(13) =262a(14) =385a(15) =565a(16) =829a(17) =1216a(18) =1783a(19) =2614a(20) =3832a(21) =5617a(22) =8233a(23) =12067a(24) =17686a(25) =25921a(26) =37990a(27) =55678a(28) =81601a(29) =119593