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 | 0 |
| 3 | 6 |
| 4 | 72 |
| 5 | 650 |
| 6 | 5400 |
| 7 | 43757 |
| 8 | 353192 |
| 9 | 2862330 |
| 10 | 23352300 |
| 11 | 191891117 |
| 12 | 1587587760 |
| 13 | 13215894133 |
| 14 | 110619113423 |
| 15 | 930376519256 |
| 16 | 7858437064232 |
| 17 | 66627124896218 |
| 18 | 566791391339532 |
| 19 | 4836144006188165 |
| 20 | 41375938305568772 |
| 21 | 354859541163656045 |