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 | -1 |
| 3 | 6 |
| 4 | -48 |
| 5 | 534 |
| 6 | -7542 |
| 7 | 129240 |
| 8 | -2603736 |
| 9 | 60292512 |
| 10 | -1577546928 |
| 11 | 46021512096 |
| 12 | -1480976147664 |
| 13 | 52110720451152 |
| 14 | -1990258155061776 |
| 15 | 81995762243700864 |
| 16 | -3624527727510038784 |
| 17 | 171109526616468957312 |
| 18 | -8591991935936929932672 |
| 19 | 457246520477143117555968 |