First differences of A081881.

Terms

a(0) =1a(1) =2a(2) =6a(3) =16a(4) =43a(5) =117a(6) =318a(7) =865a(8) =2351a(9) =6391a(10) =17372a(11) =47222a(12) =128363a(13) =348927a(14) =948482a(15) =2578241a(16) =7008386a(17) =19050768a(18) =51785356a(19) =140767193a(20) =382644902a(21) =1040136684a(22) =2827384648a(23) =7685628310a(24) =20891703776a(25) =56789538739a(26) =154369971201a(27) =419621087576