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

Terms

a(0) =1a(1) =0a(2) =2a(3) =3a(4) =10a(5) =30a(6) =77a(7) =252a(8) =682a(9) =2136a(10) =6182a(11) =18766a(12) =56173a(13) =169351a(14) =512990a(15) =1551828a(16) =4720170a(17) =14348289a(18) =43751984a(19) =133502873a(20) =408029510a(21) =1248460587a(22) =3823949824a(23) =11724787763a(24) =35980251181a(25) =110510334780a(26) =339674840715