a(n) = T(n,n), array T given by A048494.

Terms

a(0) =1a(1) =2a(2) =7a(3) =28a(4) =101a(5) =326a(6) =967a(7) =2696a(8) =7177a(9) =18442a(10) =46091a(11) =112652a(12) =270349a(13) =638990a(14) =1490959a(15) =3440656a(16) =7864337a(17) =17825810a(18) =40108051a(19) =89653268a(20) =199229461a(21) =440401942a(22) =968884247a(23) =2122317848a(24) =4630511641