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 | -2 |
| 3 | 9 |
| 4 | -56 |
| 5 | 425 |
| 6 | -3726 |
| 7 | 36652 |
| 8 | -397440 |
| 9 | 4695489 |
| 10 | -59941550 |
| 11 | 821711605 |
| 12 | -12037503384 |
| 13 | 187689245588 |
| 14 | -3104186515976 |
| 15 | 54295661153700 |
| 16 | -1001685184237056 |
| 17 | 19444296845046033 |
| 18 | -396260414466644574 |
| 19 | 8460628832978195683 |
| 20 | -188898511962856879400 |