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 | 12 |
| 2 | 132 |
| 3 | 1200 |
| 4 | 5220 |
| 5 | -132048 |
| 6 | -5451376 |
| 7 | -139104576 |
| 8 | -3034129500 |
| 9 | -61171843920 |
| 10 | -1176294856176 |
| 11 | -21916435874112 |
| 12 | -399241706218992 |
| 13 | -7151078337480000 |
| 14 | -126420386691188160 |
| 15 | -2211675290036790528 |
| 16 | -38363623542890191836 |
| 17 | -660751288131343246416 |
| 18 | -11312478475520480652400 |