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 | 3 |
| 2 | -3 |
| 3 | 15 |
| 4 | -39 |
| 5 | 123 |
| 6 | -363 |
| 7 | 1095 |
| 8 | -3279 |
| 9 | 9843 |
| 10 | -29523 |
| 11 | 88575 |
| 12 | -265719 |
| 13 | 797163 |
| 14 | -2391483 |
| 15 | 7174455 |
| 16 | -21523359 |
| 17 | 64570083 |
| 18 | -193710243 |
| 19 | 581130735 |
| 20 | -1743392199 |
| 21 | 5230176603 |
| 22 | -15690529803 |
| 23 | 47071589415 |
| 24 | -141214768239 |