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 | 0 |
| 3 | 0 |
| 4 | 0 |
| 5 | 0 |
| 6 | 1 |
| 7 | 4 |
| 8 | 12 |
| 9 | 42 |
| 10 | 137 |
| 11 | 452 |
| 12 | 1491 |
| 13 | 4994 |
| 14 | 16831 |
| 15 | 57408 |
| 16 | 197400 |
| 17 | 685008 |
| 18 | 2395310 |
| 19 | 8437830 |
| 20 | 29917709 |
| 21 | 106724174 |
| 22 | 382807427 |
| 23 | 1380058180 |
| 24 | 4998370015 |
| 25 | 18181067670 |
| 26 | 66393725289 |
| 27 | 243347195594 |
| 28 | 894959868983 |
| 29 | 3301849331598 |
| 30 | 12217869541117 |
| 31 | 45335177297876 |