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 | 30 |
| 7 | 220 |
| 8 | 1855 |
| 9 | 17304 |
| 10 | 177996 |
| 11 | 2002440 |
| 12 | 24474285 |
| 13 | 323060540 |
| 14 | 4581585866 |
| 15 | 69487385604 |
| 16 | 1122488536715 |
| 17 | 19242660629360 |
| 18 | 348933579412440 |
| 19 | 6673354706262864 |
| 20 | 134252194678935321 |
| 21 | 2834212998777523380 |
| 22 | 62651024183503148470 |
| 23 | 1447238658638922729580 |