a(n) = [x^n] Product_{k=1..n} (x^prime(k) + 1 + 1/x^prime(k)).

Terms

a(0) =1a(1) =0a(2) =1a(3) =2a(4) =3a(5) =6a(6) =16a(7) =38a(8) =91a(9) =225a(10) =547a(11) =1407a(12) =3570a(13) =9250a(14) =24578a(15) =65740a(16) =175626a(17) =470084a(18) =1279101a(19) =3482419a(20) =9547953a(21) =26445796a(22) =73251187a(23) =203818706a(24) =567543095a(25) =1577629707a(26) =4408095456a(27) =12400615844a(28) =34995570604a(29) =99241500366