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 | 0 |
| 4 | 1 |
| 5 | 4 |
| 6 | 16 |
| 7 | 64 |
| 8 | 252 |
| 9 | 1018 |
| 10 | 4182 |
| 11 | 17510 |
| 12 | 74510 |
| 13 | 322034 |
| 14 | 1410362 |
| 15 | 6251114 |
| 16 | 27998532 |
| 17 | 126583634 |
| 18 | 577079333 |
| 19 | 2650573354 |
| 20 | 12256481666 |
| 21 | 57021299394 |
| 22 | 266754944481 |
| 23 | 1254245360430 |
| 24 | 5924659521632 |
| 25 | 28105641930102 |
| 26 | 133853504339029 |
| 27 | 639801068848128 |