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 | 1 |
| 2 | -1 |
| 3 | 2 |
| 4 | -4 |
| 5 | 9 |
| 6 | -22 |
| 7 | 55 |
| 8 | -142 |
| 9 | 376 |
| 10 | -1011 |
| 11 | 2758 |
| 12 | -7614 |
| 13 | 21220 |
| 14 | -59630 |
| 15 | 168759 |
| 16 | -480533 |
| 17 | 1375676 |
| 18 | -3957075 |
| 19 | 11430582 |
| 20 | -33144264 |
| 21 | 96434321 |
| 22 | -281447954 |
| 23 | 823734157 |
| 24 | -2417092933 |
| 25 | 7109265120 |
| 26 | -20955593252 |
| 27 | 61893804180 |
| 28 | -183148075432 |
| 29 | 542885589115 |
| 30 | -1611809502764 |
| 31 | 4792612539375 |