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 | -4 |
| 3 | 23 |
| 4 | -150 |
| 5 | 1054 |
| 6 | -7761 |
| 7 | 58998 |
| 8 | -459085 |
| 9 | 3636389 |
| 10 | -29209558 |
| 11 | 237295537 |
| 12 | -1945823646 |
| 13 | 16081045446 |
| 14 | -133787515943 |
| 15 | 1119454523221 |
| 16 | -9413778489629 |
| 17 | 79510460561765 |
| 18 | -674169212593940 |
| 19 | 5736078315701995 |
| 20 | -48956250060321142 |
| 21 | 419002149097227663 |