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 | 0 |
| 3 | 0 |
| 4 | 0 |
| 5 | 1 |
| 6 | 15 |
| 7 | 140 |
| 8 | 1050 |
| 9 | 6951 |
| 10 | 42651 |
| 11 | 253660 |
| 12 | 1594230 |
| 13 | 12463451 |
| 14 | 134921787 |
| 15 | 1806386946 |
| 16 | 25524454410 |
| 17 | 354189159871 |
| 18 | 4751404201923 |
| 19 | 62042283083648 |
| 20 | 803415873180606 |
| 21 | 10624141898153091 |
| 22 | 148849893975447819 |
| 23 | 2279247411153872566 |
| 24 | 38395707003954897234 |