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 | -3 |
| 4 | -20 |
| 5 | 370 |
| 6 | -4074 |
| 7 | 34293 |
| 8 | -138312 |
| 9 | -2932533 |
| 10 | 106271090 |
| 11 | -2192834490 |
| 12 | 32208497124 |
| 13 | -206343936097 |
| 14 | -7657279887698 |
| 15 | 412496622532785 |
| 16 | -12455477719752976 |
| 17 | 260294034150380430 |
| 18 | -2256541295745391542 |
| 19 | -122593550603339550843 |
| 20 | 8728842979656718306780 |