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) |
|---|---|
| 1 | 1 |
| 2 | 1 |
| 3 | 1 |
| 4 | 1 |
| 5 | 0 |
| 6 | 1 |
| 7 | 1 |
| 8 | -1 |
| 9 | 1 |
| 10 | 2 |
| 11 | -3 |
| 12 | 5 |
| 13 | 17 |
| 14 | -91 |
| 15 | 1532 |
| 16 | 139497 |
| 17 | -213710951 |
| 18 | 29812036392235 |
| 19 | 6371158648631364574889 |
| 20 | -189937213493701003981668660072118562 |
| 21 | 1210120120447335073097142485947209203511752911347585124133 |