The matrix product A127773 * A001263 of infinite lower triangular matrices.

Terms

a(0) =1a(1) =3a(2) =3a(3) =6a(4) =18a(5) =6a(6) =10a(7) =60a(8) =60a(9) =10a(10) =15a(11) =150a(12) =300a(13) =150a(14) =15a(15) =21a(16) =315a(17) =1050a(18) =1050a(19) =315a(20) =21a(21) =28a(22) =588a(23) =2940a(24) =4900a(25) =2940a(26) =588a(27) =28a(28) =36a(29) =1008