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 | -3 |
| 3 | 3 |
| 4 | -12 |
| 5 | 30 |
| 6 | -102 |
| 7 | 318 |
| 8 | -1083 |
| 9 | 3657 |
| 10 | -12747 |
| 11 | 44715 |
| 12 | -159222 |
| 13 | 571332 |
| 14 | -2068608 |
| 15 | 7538664 |
| 16 | -27646374 |
| 17 | 101915850 |
| 18 | -377496030 |
| 19 | 1404077790 |
| 20 | -5242135728 |
| 21 | 19637862132 |
| 22 | -73793090676 |
| 23 | 278068062756 |
| 24 | -1050503580534 |
| 25 | 3977985415746 |
| 26 | -15096209345958 |
| 27 | 57403753019238 |
| 28 | -218683959367908 |