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 | 1 |
| 3 | 2 |
| 4 | 11 |
| 5 | 68 |
| 6 | 510 |
| 7 | 4712 |
| 8 | 51877 |
| 9 | 664520 |
| 10 | 9662968 |
| 11 | 156490473 |
| 12 | 2783955994 |
| 13 | 53863486240 |
| 14 | 1124886942314 |
| 15 | 25206326633070 |
| 16 | 603048386506505 |
| 17 | 15339533779133582 |
| 18 | 413338072569232815 |
| 19 | 11760801736217845686 |
| 20 | 352342902996056683824 |