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 | 2 |
| 2 | -3 |
| 3 | 19 |
| 4 | -105 |
| 5 | 690 |
| 6 | -4781 |
| 7 | 34708 |
| 8 | -260189 |
| 9 | 1999169 |
| 10 | -15660175 |
| 11 | 124596499 |
| 12 | -1004110947 |
| 13 | 8179379808 |
| 14 | -67239070867 |
| 15 | 557098881920 |
| 16 | -4647368670949 |
| 17 | 39001655222788 |
| 18 | -329048378867467 |
| 19 | 2789241880512899 |
| 20 | -23743798316713367 |
| 21 | 202894843070927860 |