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 | 3 |
| 3 | 3 |
| 4 | -7 |
| 5 | 25 |
| 6 | 267 |
| 7 | -2261 |
| 8 | -9231 |
| 9 | 284337 |
| 10 | -464365 |
| 11 | -45533741 |
| 12 | 430558185 |
| 13 | 8212158409 |
| 14 | -201645489381 |
| 15 | -1064348170245 |
| 16 | 94082272856033 |
| 17 | -489731454691487 |
| 18 | -45404775138028509 |
| 19 | 840156145287526819 |
| 20 | 20537314081214613465 |
| 21 | -913405900816937424519 |