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 | -2 |
| 2 | -2 |
| 3 | -4 |
| 4 | -10 |
| 5 | -28 |
| 6 | -84 |
| 7 | -264 |
| 8 | -858 |
| 9 | -2860 |
| 10 | -9724 |
| 11 | -33592 |
| 12 | -117572 |
| 13 | -416024 |
| 14 | -1485800 |
| 15 | -5348880 |
| 16 | -19389690 |
| 17 | -70715340 |
| 18 | -259289580 |
| 19 | -955277400 |
| 20 | -3534526380 |
| 21 | -13128240840 |
| 22 | -48932534040 |
| 23 | -182965127280 |
| 24 | -686119227300 |
| 25 | -2579808294648 |
| 26 | -9723892802904 |
| 27 | -36734706144304 |