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 | -11 |
| 4 | 47 |
| 5 | -279 |
| 6 | 2089 |
| 7 | -16057 |
| 8 | 137409 |
| 9 | -1417553 |
| 10 | 15656651 |
| 11 | -187422531 |
| 12 | 2501688463 |
| 13 | -34832785831 |
| 14 | 529520417217 |
| 15 | -8723102543009 |
| 16 | 146573712239489 |
| 17 | -2670058109819937 |
| 18 | 52017332039568019 |
| 19 | -1041334898093864443 |
| 20 | 22335551258991482991 |
| 21 | -502509800119879530551 |
| 22 | 11641825391540821682393 |