A026333 a(n) = T(3n,n), where T is the array in A026323.
1, 3, 21, 156, 1221, 9828, 80579, 669273, 5612505, 47416278, 402953376, 3440825160, 29498259546, 253737784446, 2188855109385, 18928808608996, 164046653525181
Offset: 0
This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.