Quintuple factorials, 5-factorials, n!!!!!, n!5.

Terms

a(0) =1a(1) =1a(2) =2a(3) =3a(4) =4a(5) =5a(6) =6a(7) =14a(8) =24a(9) =36a(10) =50a(11) =66a(12) =168a(13) =312a(14) =504a(15) =750a(16) =1056a(17) =2856a(18) =5616a(19) =9576a(20) =15000a(21) =22176a(22) =62832a(23) =129168a(24) =229824a(25) =375000a(26) =576576a(27) =1696464a(28) =3616704a(29) =6664896