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 | 4 |
| 2 | 8 |
| 3 | 20 |
| 4 | 84 |
| 5 | 456 |
| 6 | 2860 |
| 7 | 19708 |
| 8 | 145120 |
| 9 | 1122680 |
| 10 | 9023784 |
| 11 | 74777248 |
| 12 | 635292016 |
| 13 | 5510485600 |
| 14 | 48644137764 |
| 15 | 435920025116 |
| 16 | 3957758805776 |
| 17 | 36345636909032 |
| 18 | 337159090063880 |
| 19 | 3155827384249824 |
| 20 | 29776934546342464 |
| 21 | 283001546964599248 |