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 | 5 |
| 3 | -9 |
| 4 | 27 |
| 5 | -61 |
| 6 | 159 |
| 7 | -385 |
| 8 | 967 |
| 9 | -2385 |
| 10 | 5935 |
| 11 | -14705 |
| 12 | 36511 |
| 13 | -90561 |
| 14 | 224735 |
| 15 | -557569 |
| 16 | 1383487 |
| 17 | -3432641 |
| 18 | 8517119 |
| 19 | -21132545 |
| 20 | 52434047 |
| 21 | -130098945 |
| 22 | 322800895 |
| 23 | -800931585 |
| 24 | 1987267071 |
| 25 | -4930795521 |
| 26 | 12234262015 |
| 27 | -30355580929 |
| 28 | 75318094847 |
| 29 | -186878827521 |
| 30 | 463682682879 |