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) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 2 |
| 3 | 7 |
| 4 | 35 |
| 5 | 228 |
| 6 | 1834 |
| 7 | 17582 |
| 8 | 195866 |
| 9 | 2487832 |
| 10 | 35499576 |
| 11 | 562356672 |
| 12 | 9794156448 |
| 13 | 186025364016 |
| 14 | 3826961710272 |
| 15 | 84775065603888 |
| 16 | 2011929826983504 |
| 17 | 50929108873336320 |
| 18 | 1369732445916318336 |
| 19 | 39005083331889816960 |
| 20 | 1172419218038422659456 |
| 21 | 37095226237402478348544 |