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 | -2 |
| 4 | -4 |
| 5 | -14 |
| 6 | -38 |
| 7 | -132 |
| 8 | -420 |
| 9 | -1426 |
| 10 | -4834 |
| 11 | -16796 |
| 12 | -58688 |
| 13 | -208012 |
| 14 | -742636 |
| 15 | -2674384 |
| 16 | -9693976 |
| 17 | -35357670 |
| 18 | -129641774 |
| 19 | -477638700 |
| 20 | -1767253368 |
| 21 | -6564119892 |
| 22 | -24466233428 |
| 23 | -91482563640 |
| 24 | -343059494120 |
| 25 | -1289904147128 |
| 26 | -4861945985428 |
| 27 | -18367353066440 |
| 28 | -69533549429280 |
| 29 | -263747951750360 |
| 30 | -1002242211282032 |