A024581 / [1,2,3,...].

Terms

a(0) =1a(1) =1a(2) =3a(3) =9a(4) =24a(5) =65a(6) =177a(7) =481a(8) =1308a(9) =3555a(10) =9664a(11) =26269a(12) =71406a(13) =194103a(14) =527625a(15) =1434235a(16) =3898654a(17) =10597641a(18) =28807374a(19) =78306562a(20) =212859305a(21) =578611580a(22) =1572829344a(23) =4275393425a(24) =11621724256a(25) =31591121861a(26) =85873572496a(27) =233428571660a(28) =634524644587