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 | 1 |
| 2 | -1 |
| 3 | 2 |
| 4 | -4 |
| 5 | 9 |
| 6 | -21 |
| 7 | 51 |
| 8 | -127 |
| 9 | 323 |
| 10 | -835 |
| 11 | 2188 |
| 12 | -5798 |
| 13 | 15511 |
| 14 | -41835 |
| 15 | 113634 |
| 16 | -310572 |
| 17 | 853467 |
| 18 | -2356779 |
| 19 | 6536382 |
| 20 | -18199284 |
| 21 | 50852019 |
| 22 | -142547559 |
| 23 | 400763223 |
| 24 | -1129760415 |
| 25 | 3192727797 |
| 26 | -9043402501 |
| 27 | 25669818476 |
| 28 | -73007772802 |