For definition see comments lines.

Terms

a(0) =1a(1) =6a(2) =6a(3) =72a(4) =72a(5) =72a(6) =6a(7) =72a(8) =72a(9) =5184a(10) =6a(11) =5184a(12) =72a(13) =5184a(14) =31104a(15) =5184a(16) =5184a(17) =5184a(18) =2592a(19) =5184a(20) =432a(21) =373248a(22) =36a(23) =373248a(24) =31104a(25) =26873856a(26) =26873856a(27) =26873856a(28) =373248a(29) =31104