Irregular table: T(n,k) equals the number of alignments of length k of n strings each of length 3.

Terms

a(0) =1a(1) =1a(2) =12a(3) =30a(4) =20a(5) =1a(6) =60a(7) =690a(8) =2940a(9) =5670a(10) =5040a(11) =1680a(12) =1a(13) =252a(14) =8730a(15) =103820a(16) =581700a(17) =1767360a(18) =3087000a(19) =3099600a(20) =1663200a(21) =369600a(22) =1a(23) =1020a(24) =94890a(25) =2615340a(26) =32186070a(27) =214628400a(28) =859992000a(29) =2189325600