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 | 5 |
| 3 | 23 |
| 4 | 112 |
| 5 | 558 |
| 6 | 2790 |
| 7 | 13951 |
| 8 | 69755 |
| 9 | 348773 |
| 10 | 1743862 |
| 11 | 8719308 |
| 12 | 43596540 |
| 13 | 217982701 |
| 14 | 1089913505 |
| 15 | 5449567523 |
| 16 | 27247837612 |
| 17 | 136239188058 |
| 18 | 681195940290 |
| 19 | 3405979701451 |
| 20 | 17029898507255 |
| 21 | 85149492536273 |