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 | 2 |
| 3 | -7 |
| 4 | 20 |
| 5 | -31 |
| 6 | 2 |
| 7 | -127 |
| 8 | 1640 |
| 9 | -511 |
| 10 | -49498 |
| 11 | -2047 |
| 12 | 2706860 |
| 13 | -8191 |
| 14 | -199344598 |
| 15 | -32767 |
| 16 | 19391577680 |
| 17 | -131071 |
| 18 | -2404879413298 |
| 19 | -524287 |
| 20 | 370371189286100 |
| 21 | -2097151 |
| 22 | -69348874388943598 |
| 23 | -8388607 |
| 24 | 15514534163573864120 |
| 25 | -33554431 |
| 26 | -4087072509293056783498 |