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 | 10 |
| 4 | -72 |
| 5 | 644 |
| 6 | -6704 |
| 7 | 78408 |
| 8 | -1008480 |
| 9 | 14065744 |
| 10 | -210682080 |
| 11 | 3365194560 |
| 12 | -57019105920 |
| 13 | 1020662366400 |
| 14 | -19238635678208 |
| 15 | 380825404556288 |
| 16 | -7898501807543808 |
| 17 | 171304216873595136 |
| 18 | -3878189367387230720 |