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.
| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 1 |
| 3 | 4 |
| 4 | 26 |
| 5 | 236 |
| 6 | 2760 |
| 7 | 39572 |
| 8 | 672592 |
| 9 | 13227804 |
| 10 | 295579520 |
| 11 | 7398318500 |
| 12 | 205075286784 |
| 13 | 6236796259916 |
| 14 | 206489747516416 |
| 15 | 7393749269685300 |
| 16 | 284714599444490240 |
| 17 | 11733037015160276348 |
| 18 | 515240326393584058368 |
| 19 | 24019843795708471562564 |
| 20 | 1184776250223810469888000 |