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 | 16 |
| 3 | 64 |
| 4 | 232 |
| 5 | 544 |
| 6 | -1664 |
| 7 | -37376 |
| 8 | -362024 |
| 9 | -2743712 |
| 10 | -17780864 |
| 11 | -98955776 |
| 12 | -442825664 |
| 13 | -1129423616 |
| 14 | 5536033792 |
| 15 | 118591811584 |
| 16 | 1224814969816 |
| 17 | 9905491019104 |
| 18 | 68032143081856 |
| 19 | 398051159254528 |
| 20 | 1854461906222272 |
| 21 | 4784426026102528 |