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) |
|---|---|
| 1 | 1 |
| 2 | 0 |
| 3 | 9 |
| 4 | -52 |
| 5 | 520 |
| 6 | -6636 |
| 7 | 102984 |
| 8 | -1864600 |
| 9 | 38741463 |
| 10 | -909081740 |
| 11 | 23775986069 |
| 12 | -685854111804 |
| 13 | 21633935838489 |
| 14 | -740800448012044 |
| 15 | 27368368159530285 |
| 16 | -1085102592823737200 |
| 17 | 45957792326631241516 |
| 18 | -2070863582899905915336 |
| 19 | 98920982783031811482920 |
| 20 | -4993219047619535240997780 |