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 | 0 |
| 3 | -3 |
| 4 | -4 |
| 5 | 15 |
| 6 | 48 |
| 7 | -105 |
| 8 | -624 |
| 9 | 945 |
| 10 | 9600 |
| 11 | -10395 |
| 12 | -175680 |
| 13 | 135135 |
| 14 | 3790080 |
| 15 | -2027025 |
| 16 | -95235840 |
| 17 | 34459425 |
| 18 | 2752081920 |
| 19 | -654729075 |
| 20 | -90328089600 |
| 21 | 13749310575 |
| 22 | 3328103116800 |
| 23 | -316234143225 |
| 24 | -136191650918400 |
| 25 | 7905853580625 |
| 26 | 6131573025177600 |
| 27 | -213458046676875 |
| 28 | -301213549769932800 |