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 | 2 |
| 2 | 12 |
| 3 | 56 |
| 4 | 240 |
| 5 | 992 |
| 6 | 4032 |
| 7 | 16256 |
| 8 | 65280 |
| 9 | 261632 |
| 10 | 1047552 |
| 11 | 4192256 |
| 12 | 16773120 |
| 13 | 67100672 |
| 14 | 268419072 |
| 15 | 1073709056 |
| 16 | 4294901760 |
| 17 | 17179738112 |
| 18 | 68719214592 |
| 19 | 274877382656 |
| 20 | 1099510579200 |
| 21 | 4398044413952 |
| 22 | 17592181850112 |
| 23 | 70368735789056 |
| 24 | 281474959933440 |