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) |
|---|---|
| 0 | 0 |
| 1 | 0 |
| 2 | 0 |
| 3 | 6 |
| 4 | 72 |
| 5 | 630 |
| 6 | 4680 |
| 7 | 31206 |
| 8 | 193032 |
| 9 | 1131990 |
| 10 | 6386760 |
| 11 | 35025606 |
| 12 | 188061192 |
| 13 | 993760950 |
| 14 | 5187840840 |
| 15 | 26831095206 |
| 16 | 137770476552 |
| 17 | 703455087510 |
| 18 | 3576115150920 |
| 19 | 18117222864006 |
| 20 | 91536570671112 |
| 21 | 461496288791670 |
| 22 | 2322770028381000 |
| 23 | 11675109032796006 |