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 | 13 |
| 4 | 65 |
| 5 | 221 |
| 6 | -2933 |
| 7 | -120903 |
| 8 | -3104127 |
| 9 | -71637191 |
| 10 | -1562635789 |
| 11 | -31373685947 |
| 12 | -505087300991 |
| 13 | -1692007785259 |
| 14 | 402032879446395 |
| 15 | 28152810613025521 |
| 16 | 1423083552938781697 |
| 17 | 62552808878706976625 |
| 18 | 2459148829654813484131 |
| 19 | 82692880516086149155581 |