Main diagonal of square table A322200.

Terms

a(0) =0a(1) =2a(2) =10a(3) =26a(4) =90a(5) =262a(6) =994a(7) =3446a(8) =13050a(9) =48698a(10) =185310a(11) =705454a(12) =2706354a(13) =10400626a(14) =40123534a(15) =155118406a(16) =601106490a(17) =2333606254a(18) =9075235522a(19) =35345263838a(20) =137846899790a(21) =538257884918