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 | 0 |
| 2 | -1 |
| 3 | -5 |
| 4 | -26 |
| 5 | -154 |
| 6 | -1044 |
| 7 | -8028 |
| 8 | -69264 |
| 9 | -663696 |
| 10 | -6999840 |
| 11 | -80627040 |
| 12 | -1007441280 |
| 13 | -13575738240 |
| 14 | -196287356160 |
| 15 | -3031488633600 |
| 16 | -49811492505600 |
| 17 | -867718162483200 |
| 18 | -15974614352793600 |
| 19 | -309920046408806400 |
| 20 | -6320046028584960000 |