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 | -2 |
| 3 | 4 |
| 4 | 16 |
| 5 | -32 |
| 6 | -128 |
| 7 | -512 |
| 8 | 4096 |
| 9 | -8192 |
| 10 | -32768 |
| 11 | -131072 |
| 12 | 1048576 |
| 13 | 4194304 |
| 14 | -33554432 |
| 15 | 268435456 |
| 16 | 4294967296 |
| 17 | -8589934592 |
| 18 | -34359738368 |
| 19 | -137438953472 |
| 20 | 1099511627776 |
| 21 | 4398046511104 |
| 22 | -35184372088832 |
| 23 | 281474976710656 |