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 | 1 |
| 3 | 2 |
| 4 | 15 |
| 5 | 104 |
| 6 | 695 |
| 7 | 5004 |
| 8 | 40271 |
| 9 | 362816 |
| 10 | 3628719 |
| 11 | 39916700 |
| 12 | 479001479 |
| 13 | 6227020656 |
| 14 | 87178291031 |
| 15 | 1307674367804 |
| 16 | 20922789887775 |
| 17 | 355687428095744 |
| 18 | 6402373705727711 |
| 19 | 121645100408831676 |
| 20 | 2432902008176639639 |
| 21 | 51090942171709439600 |
| 22 | 1124000727777607679559 |
| 23 | 25852016738884976639516 |