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 | 1 |
| 4 | -4 |
| 5 | 21 |
| 6 | -126 |
| 7 | 1023 |
| 8 | -8240 |
| 9 | 84745 |
| 10 | -864370 |
| 11 | 10925883 |
| 12 | -133566808 |
| 13 | 1994183205 |
| 14 | -28455880012 |
| 15 | 489891177051 |
| 16 | -8112780640000 |
| 17 | 158096182329585 |
| 18 | -2911196026492074 |
| 19 | 64115697136312563 |
| 20 | -1328879415116924744 |
| 21 | 31920276313015362525 |
| 22 | -728711636884140292372 |