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 | 0 |
| 1 | 1 |
| 2 | -1 |
| 3 | 2 |
| 4 | 0 |
| 5 | 9 |
| 6 | 35 |
| 7 | 230 |
| 8 | 1624 |
| 9 | 13209 |
| 10 | 120287 |
| 11 | 1214674 |
| 12 | 13469896 |
| 13 | 162744945 |
| 14 | 2128047987 |
| 15 | 29943053062 |
| 16 | 451123462672 |
| 17 | 7245940789073 |
| 18 | 123604151490591 |
| 19 | 2231697509543362 |
| 20 | 42519034050101744 |
| 21 | 852495597142800377 |
| 22 | 17942811657908144163 |
| 23 | 395553947953212635718 |
| 24 | 9114871523102565301544 |
| 25 | 219135339782236105192745 |