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 | -1 |
| 4 | 25 |
| 5 | 19 |
| 6 | -209 |
| 7 | -2269 |
| 8 | 2801 |
| 9 | 68615 |
| 10 | 371071 |
| 11 | -2499641 |
| 12 | -28306871 |
| 13 | -58645861 |
| 14 | 1964456495 |
| 15 | 15133179179 |
| 16 | -37119981599 |
| 17 | -1861550428529 |
| 18 | -9225044407169 |
| 19 | 110317002942095 |
| 20 | 2150185424201081 |
| 21 | 3953685082287779 |
| 22 | -233260896605772881 |
| 23 | -2920858244957587661 |
| 24 | 7649165533910291665 |