Convolution of A000107 and A027852.

Terms

a(0) =0a(1) =0a(2) =1a(3) =3a(4) =10a(5) =30a(6) =91a(7) =268a(8) =790a(9) =2308a(10) =6737a(11) =19609a(12) =57044a(13) =165796a(14) =481823a(15) =1400028a(16) =4068577a(17) =11825459a(18) =34380152a(19) =99981942a(20) =290854486a(21) =846397344a(22) =2463892294a(23) =7174933683a(24) =20900764811a(25) =60904875999a(26) =177535250815a(27) =517673673674