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 | 0 |
| 2 | 1 |
| 3 | 6 |
| 4 | 15 |
| 5 | 60 |
| 6 | 555 |
| 7 | 3150 |
| 8 | 17745 |
| 9 | 158760 |
| 10 | 1399545 |
| 11 | 10914750 |
| 12 | 102920895 |
| 13 | 1104323220 |
| 14 | 11249313075 |
| 15 | 119330961750 |
| 16 | 1426411411425 |
| 17 | 17429852840400 |
| 18 | 213417453474225 |
| 19 | 2791671804271350 |
| 20 | 38524272522310575 |
| 21 | 537569719902715500 |
| 22 | 7732658753799054075 |