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 | 1 |
| 2 | 0 |
| 3 | 2 |
| 4 | 0 |
| 5 | 15 |
| 6 | 40 |
| 7 | 153 |
| 8 | 480 |
| 9 | 1841 |
| 10 | 6528 |
| 11 | 23901 |
| 12 | 87040 |
| 13 | 322875 |
| 14 | 1198080 |
| 15 | 4474738 |
| 16 | 16773120 |
| 17 | 63164175 |
| 18 | 238605640 |
| 19 | 904213989 |
| 20 | 3435921408 |
| 21 | 13089461538 |
| 22 | 49977753600 |
| 23 | 191219550297 |
| 24 | 733007052640 |
| 25 | 2814750270420 |
| 26 | 10825959997440 |
| 27 | 41699998413248 |
| 28 | 160842834247680 |