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 | 4 |
| 3 | 15 |
| 4 | 84 |
| 5 | 470 |
| 6 | 3552 |
| 7 | 26796 |
| 8 | 255840 |
| 9 | 2435184 |
| 10 | 28114560 |
| 11 | 323405280 |
| 12 | 4380445440 |
| 13 | 59105255040 |
| 14 | 918796677120 |
| 15 | 14228252640000 |
| 16 | 249644312064000 |
| 17 | 4363865549568000 |
| 18 | 85297521899520000 |
| 19 | 1661265370695168000 |