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 | 1 |
| 2 | 2 |
| 3 | 6 |
| 4 | 24 |
| 5 | 112 |
| 6 | 572 |
| 7 | 3116 |
| 8 | 17871 |
| 9 | 106959 |
| 10 | 663526 |
| 11 | 4243490 |
| 12 | 27856087 |
| 13 | 187029655 |
| 14 | 1280660596 |
| 15 | 8921737864 |
| 16 | 63108620169 |
| 17 | 452503644985 |
| 18 | 3284213633684 |
| 19 | 24098433889312 |
| 20 | 178583179551488 |
| 21 | 1335346240984360 |