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 | 4 |
| 3 | -8 |
| 4 | 20 |
| 5 | -44 |
| 6 | 100 |
| 7 | -220 |
| 8 | 484 |
| 9 | -1052 |
| 10 | 2276 |
| 11 | -4892 |
| 12 | 10468 |
| 13 | -22300 |
| 14 | 47332 |
| 15 | -100124 |
| 16 | 211172 |
| 17 | -444188 |
| 18 | 932068 |
| 19 | -1951516 |
| 20 | 4077796 |
| 21 | -8505116 |
| 22 | 17709284 |
| 23 | -36816668 |
| 24 | 76429540 |
| 25 | -158451484 |
| 26 | 328087780 |
| 27 | -678545180 |
| 28 | 1401829604 |