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) |
|---|---|
| 1 | 1 |
| 2 | 1 |
| 3 | -15 |
| 4 | 209 |
| 5 | -2911 |
| 6 | 40545 |
| 7 | -564719 |
| 8 | 7865521 |
| 9 | -109552575 |
| 10 | 1525870529 |
| 11 | -21252634831 |
| 12 | 296011017105 |
| 13 | -4122901604639 |
| 14 | 57424611447841 |
| 15 | -799821658665135 |
| 16 | 11140078609864049 |
| 17 | -155161278879431551 |
| 18 | 2161117825702177665 |
| 19 | -30100488280951055759 |
| 20 | 419245718107612602961 |