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 | 0 |
| 1 | 1 |
| 2 | 1 |
| 3 | 3 |
| 4 | -2 |
| 5 | 25 |
| 6 | -129 |
| 7 | 931 |
| 8 | -7412 |
| 9 | 66753 |
| 10 | -667475 |
| 11 | 7342291 |
| 12 | -88107414 |
| 13 | 1145396473 |
| 14 | -16035550517 |
| 15 | 240533257875 |
| 16 | -3848532125864 |
| 17 | 65425046139841 |
| 18 | -1177650830516967 |
| 19 | 22375365779822563 |
| 20 | -447507315596451050 |
| 21 | 9397653627525472281 |
| 22 | -206748379805560389929 |