Nonuple factorial, 9-factorial, n!9, n!!!!!!!!!.

Terms

a(0) =1a(1) =1a(2) =2a(3) =3a(4) =4a(5) =5a(6) =6a(7) =7a(8) =8a(9) =9a(10) =10a(11) =22a(12) =36a(13) =52a(14) =70a(15) =90a(16) =112a(17) =136a(18) =162a(19) =190a(20) =440a(21) =756a(22) =1144a(23) =1610a(24) =2160a(25) =2800a(26) =3536a(27) =4374a(28) =5320a(29) =12760