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 | -18 |
| 2 | 126 |
| 3 | -420 |
| 4 | 630 |
| 5 | -252 |
| 6 | -84 |
| 7 | -72 |
| 8 | -90 |
| 9 | -140 |
| 10 | -252 |
| 11 | -504 |
| 12 | -1092 |
| 13 | -2520 |
| 14 | -6120 |
| 15 | -15504 |
| 16 | -40698 |
| 17 | -110124 |
| 18 | -305900 |
| 19 | -869400 |
| 20 | -2521260 |
| 21 | -7443720 |
| 22 | -22331160 |
| 23 | -67964400 |
| 24 | -209556900 |
| 25 | -653817528 |
| 26 | -2062039896 |
| 27 | -6567978928 |
| 28 | -21111360840 |