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 | -1 |
| 3 | 5 |
| 4 | 11 |
| 5 | -91 |
| 6 | -301 |
| 7 | 3485 |
| 8 | 15371 |
| 9 | -228811 |
| 10 | -1261501 |
| 11 | 22951565 |
| 12 | 151846331 |
| 13 | -3264973531 |
| 14 | -25201039501 |
| 15 | 625232757245 |
| 16 | 5515342166891 |
| 17 | -155079142742251 |
| 18 | -1538993024478301 |
| 19 | 48364005482108525 |
| 20 | 533289474412481051 |
| 21 | -18523127502677822971 |