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 | -4 |
| 2 | 15 |
| 3 | -56 |
| 4 | 209 |
| 5 | -780 |
| 6 | 2911 |
| 7 | -10864 |
| 8 | 40545 |
| 9 | -151316 |
| 10 | 564719 |
| 11 | -2107560 |
| 12 | 7865521 |
| 13 | -29354524 |
| 14 | 109552575 |
| 15 | -408855776 |
| 16 | 1525870529 |
| 17 | -5694626340 |
| 18 | 21252634831 |
| 19 | -79315912984 |
| 20 | 296011017105 |
| 21 | -1104728155436 |
| 22 | 4122901604639 |
| 23 | -15386878263120 |
| 24 | 57424611447841 |