First differences of A000543.

Terms

a(0) =1a(1) =22a(2) =310a(3) =2583a(4) =13809a(5) =54186a(6) =171002a(7) =460055a(8) =1096313a(9) =2375494a(10) =4768246a(11) =8988607a(12) =16078425a(13) =27509418a(14) =45304554a(15) =72180431a(16) =111712337a(17) =168523670a(18) =248501398a(19) =359039239a(20) =509310241a(21) =710570442a(22) =976495290a(23) =1323550503