a(n) = binomial(n,22).

Terms

a(0) =1a(1) =23a(2) =276a(3) =2300a(4) =14950a(5) =80730a(6) =376740a(7) =1560780a(8) =5852925a(9) =20160075a(10) =64512240a(11) =193536720a(12) =548354040a(13) =1476337800a(14) =3796297200a(15) =9364199760a(16) =22239974430a(17) =51021117810a(18) =113380261800a(19) =244662670200a(20) =513791607420