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 | 0 |
| 4 | 0 |
| 5 | 0 |
| 6 | 3 |
| 7 | 14 |
| 8 | 78 |
| 9 | 497 |
| 10 | 3628 |
| 11 | 29990 |
| 12 | 277200 |
| 13 | 2834328 |
| 14 | 31770514 |
| 15 | 387459072 |
| 16 | 5108103000 |
| 17 | 72397196844 |
| 18 | 1097800704000 |
| 19 | 17735107218083 |
| 20 | 304112751022080 |
| 21 | 5516784599040000 |
| 22 | 105559797875432727 |
| 23 | 2124765080865042873 |
| 24 | 44881973505008640000 |
| 25 | 992717442773183102976 |