"INVERT" transform of squares A000290.

Terms

a(0) =1a(1) =5a(2) =18a(3) =63a(4) =221a(5) =776a(6) =2725a(7) =9569a(8) =33602a(9) =117995a(10) =414345a(11) =1454992a(12) =5109273a(13) =17941453a(14) =63002258a(15) =221235399a(16) =776878533a(17) =2728045592a(18) =9579660701a(19) =33639430153a(20) =118126444802a(21) =414806579603