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 | 3 |
| 5 | 20 |
| 6 | 130 |
| 7 | 924 |
| 8 | 7413 |
| 9 | 66744 |
| 10 | 667476 |
| 11 | 7342280 |
| 12 | 88107415 |
| 13 | 1145396460 |
| 14 | 16035550518 |
| 15 | 240533257860 |
| 16 | 3848532125865 |
| 17 | 65425046139824 |
| 18 | 1177650830516968 |
| 19 | 22375365779822544 |
| 20 | 447507315596451051 |
| 21 | 9397653627525472260 |
| 22 | 206748379805560389930 |
| 23 | 4755212735527888968620 |