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 | 1 |
| 1 | 0 |
| 2 | 0 |
| 3 | 1 |
| 4 | 3 |
| 5 | 13 |
| 6 | 67 |
| 7 | 425 |
| 8 | 3103 |
| 9 | 25751 |
| 10 | 239483 |
| 11 | 2466678 |
| 12 | 27873456 |
| 13 | 342843514 |
| 14 | 4559818741 |
| 15 | 65205407995 |
| 16 | 997642742322 |
| 17 | 16261576699844 |
| 18 | 281325276907304 |
| 19 | 5148252567403659 |
| 20 | 99361274550890613 |
| 21 | 2017033873383079454 |