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 | 1 |
| 2 | 5 |
| 3 | 30 |
| 4 | 220 |
| 5 | 1725 |
| 6 | 14356 |
| 7 | 124020 |
| 8 | 1102770 |
| 9 | 10023680 |
| 10 | 92722620 |
| 11 | 870039474 |
| 12 | 8261024380 |
| 13 | 79225392830 |
| 14 | 766302511445 |
| 15 | 7466883915800 |
| 16 | 73227699088806 |
| 17 | 722228333119200 |
| 18 | 7159117292177840 |
| 19 | 71284856957207030 |
| 20 | 712673042497177450 |