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 | -7 |
| 3 | -23 |
| 4 | 145 |
| 5 | 881 |
| 6 | -4919 |
| 7 | -47207 |
| 8 | 228257 |
| 9 | 3249505 |
| 10 | -13184999 |
| 11 | -273145399 |
| 12 | 887134513 |
| 13 | 27109092817 |
| 14 | -65152896535 |
| 15 | -3101371292039 |
| 16 | 4716976292161 |
| 17 | 401692501673153 |
| 18 | -239816274060743 |
| 19 | -58083536514994775 |
| 20 | -21631462857761839 |
| 21 | 9271734379541402161 |