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 | 1 |
| 3 | 20 |
| 4 | 204 |
| 5 | 1689 |
| 6 | 13303 |
| 7 | 90614 |
| 8 | 543116 |
| 9 | 2842431 |
| 10 | 13218770 |
| 11 | 55233883 |
| 12 | 210199115 |
| 13 | 736166006 |
| 14 | 2395665563 |
| 15 | 7301022565 |
| 16 | 20981692199 |
| 17 | 57188601747 |
| 18 | 148588072319 |
| 19 | 369611918382 |
| 20 | 883579452509 |
| 21 | 2036672785494 |
| 22 | 4539872512172 |
| 23 | 9811474182969 |
| 24 | 20605911433906 |
| 25 | 42141179374995 |