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 | 2 |
| 1 | 6 |
| 2 | 20 |
| 3 | 72 |
| 4 | 272 |
| 5 | 1056 |
| 6 | 4160 |
| 7 | 16512 |
| 8 | 65792 |
| 9 | 262656 |
| 10 | 1049600 |
| 11 | 4196352 |
| 12 | 16781312 |
| 13 | 67117056 |
| 14 | 268451840 |
| 15 | 1073774592 |
| 16 | 4295032832 |
| 17 | 17180000256 |
| 18 | 68719738880 |
| 19 | 274878431232 |
| 20 | 1099512676352 |
| 21 | 4398048608256 |
| 22 | 17592190238720 |
| 23 | 70368752566272 |