Convolution of A000081 and A027852, shifted by 3 leading zeros.

Terms

a(0) =1a(1) =2a(2) =6a(3) =15a(4) =41a(5) =106a(6) =284a(7) =750a(8) =2010a(9) =5382a(10) =14523a(11) =39290a(12) =106854a(13) =291552a(14) =798675a(15) =2194828a(16) =6051153a(17) =16730373a(18) =46383002a(19) =128910484a(20) =359115067a(21) =1002575810a(22) =2804667061a(23) =7860780578a(24) =22070885735a(25) =62071872704a(26) =174842835886a(27) =493217417610