A177630 Number of permutations of 3 copies of 1..n avoiding adjacent step pattern up, up, down, down, down, down.
1, 1, 20, 1680, 369600, 167895912, 136567215720, 180834782762247, 364064983677371040
Offset: 0
Crossrefs
Cf. A014606.
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.