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 | 5 |
| 3 | 20 |
| 4 | 105 |
| 5 | 520 |
| 6 | 2605 |
| 7 | 13020 |
| 8 | 65105 |
| 9 | 325520 |
| 10 | 1627605 |
| 11 | 8138020 |
| 12 | 40690105 |
| 13 | 203450520 |
| 14 | 1017252605 |
| 15 | 5086263020 |
| 16 | 25431315105 |
| 17 | 127156575520 |
| 18 | 635782877605 |
| 19 | 3178914388020 |
| 20 | 15894571940105 |
| 21 | 79472859700520 |