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 | 2 |
| 2 | 5 |
| 3 | 15 |
| 4 | 49 |
| 5 | 140 |
| 6 | -64 |
| 7 | -8540 |
| 8 | -146124 |
| 9 | -2124936 |
| 10 | -30374136 |
| 11 | -445116672 |
| 12 | -6793958016 |
| 13 | -108691150464 |
| 14 | -1826654613120 |
| 15 | -32257962443520 |
| 16 | -598196854045440 |
| 17 | -11635261535301120 |
| 18 | -237044583523514880 |
| 19 | -5050811716879104000 |