a(n) = T(n,n), array T given by A047858.

Terms

a(0) =1a(1) =3a(2) =11a(3) =34a(4) =93a(5) =236a(6) =571a(7) =1338a(8) =3065a(9) =6904a(10) =15351a(11) =33782a(12) =73717a(13) =159732a(14) =344051a(15) =737266a(16) =1572849a(17) =3342320a(18) =7077871a(19) =14942190a(20) =31457261a(21) =66060268a(22) =138412011a(23) =289406954a(24) =603979753a(25) =1258291176a(26) =2617245671a(27) =5435817958a(28) =11274289125a(29) =23353884644