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 | 4 |
| 2 | 20 |
| 3 | 72 |
| 4 | 280 |
| 5 | 1040 |
| 6 | 4200 |
| 7 | 16408 |
| 8 | 65840 |
| 9 | 262296 |
| 10 | 1049680 |
| 11 | 4194344 |
| 12 | 16782000 |
| 13 | 67108912 |
| 14 | 268451960 |
| 15 | 1073744160 |
| 16 | 4295033440 |
| 17 | 17179869248 |
| 18 | 68719747320 |
| 19 | 274877907016 |
| 20 | 1099512679520 |
| 21 | 4398046544304 |
| 22 | 17592190238920 |
| 23 | 70368744177752 |