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 | 1 |
| 1 | 0 |
| 2 | 0 |
| 3 | 0 |
| 4 | 1 |
| 5 | 4 |
| 6 | 23 |
| 7 | 143 |
| 8 | 1027 |
| 9 | 8370 |
| 10 | 76527 |
| 11 | 776207 |
| 12 | 8649165 |
| 13 | 105025575 |
| 14 | 1380336141 |
| 15 | 19521896861 |
| 16 | 295617295326 |
| 17 | 4772107767405 |
| 18 | 81807561726950 |
| 19 | 1484222905617529 |
| 20 | 28412267050392705 |
| 21 | 572304236300767347 |