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 | 3 |
| 4 | -1 |
| 5 | -1 |
| 6 | 9 |
| 7 | -3 |
| 8 | -1 |
| 9 | -1 |
| 10 | 27 |
| 11 | -9 |
| 12 | -3 |
| 13 | -1 |
| 14 | -1 |
| 15 | 81 |
| 16 | -27 |
| 17 | -9 |
| 18 | -3 |
| 19 | -1 |
| 20 | -1 |
| 21 | 243 |
| 22 | -81 |
| 23 | -27 |
| 24 | -9 |
| 25 | -3 |
| 26 | -1 |
| 27 | -1 |
| 28 | 729 |
| 29 | -243 |
| 30 | -81 |
| 31 | -27 |
| 32 | -9 |
| 33 | -3 |
| 34 | -1 |
| 35 | -1 |
| 36 | 2187 |
| 37 | -729 |
| 38 | -243 |
| 39 | -81 |
| 40 | -27 |
| 41 | -9 |
| 42 | -3 |
| 43 | -1 |
| 44 | -1 |
| 45 | 6561 |
| 46 | -2187 |
| 47 | -729 |
| 48 | -243 |
| 49 | -81 |
| 50 | -27 |
| 51 | -9 |
| 52 | -3 |
| 53 | -1 |
| 54 | -1 |
| 55 | 19683 |
| 56 | -6561 |
| 57 | -2187 |