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 | 4 |
| 2 | 5 |
| 3 | -3 |
| 4 | 4 |
| 5 | -8 |
| 6 | 20 |
| 7 | -52 |
| 8 | 72 |
| 9 | 936 |
| 10 | -17568 |
| 11 | 238752 |
| 12 | -3113280 |
| 13 | 41503680 |
| 14 | -577877760 |
| 15 | 8470414080 |
| 16 | -131039838720 |
| 17 | 2139954163200 |
| 18 | -36854615347200 |
| 19 | 668374040678400 |
| 20 | -12742107588403200 |
| 21 | 254904791591116800 |
| 22 | -5341386032640000000 |
| 23 | 117034910701793280000 |