a(n) is the number of distinct arrangements of the letters in the English word for n.

Terms

a(0) =6a(1) =6a(2) =60a(3) =24a(4) =24a(5) =6a(6) =60a(7) =120a(8) =12a(9) =6a(10) =120a(11) =360a(12) =10080a(13) =20160a(14) =1260a(15) =2520a(16) =7560a(17) =6720a(18) =1120a(19) =360a(20) =45360a(21) =30240a(22) =1108800a(23) =1814400a(24) =907200a(25) =181440a(26) =1663200a(27) =3326400a(28) =151200a(29) =360