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 | 3 |
| 2 | 7 |
| 3 | 21 |
| 4 | 56 |
| 5 | 168 |
| 6 | 504 |
| 7 | 1736 |
| 8 | 5208 |
| 9 | 15624 |
| 10 | 57288 |
| 11 | 171864 |
| 12 | 671832 |
| 13 | 2234232 |
| 14 | 7390152 |
| 15 | 32023992 |
| 16 | 96071976 |
| 17 | 450799272 |
| 18 | 1559322072 |
| 19 | 5860390536 |
| 20 | 20271186936 |
| 21 | 95118646392 |
| 22 | 385152551784 |
| 23 | 1236542403096 |
| 24 | 6182712015480 |
| 25 | 23494305658824 |
| 26 | 82848341007432 |
| 27 | 409295535424776 |