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 | 2 |
| 3 | 6 |
| 4 | 27 |
| 5 | 135 |
| 6 | 810 |
| 7 | 5670 |
| 8 | 45465 |
| 9 | 409185 |
| 10 | 4091850 |
| 11 | 45010350 |
| 12 | 540134595 |
| 13 | 7021749735 |
| 14 | 98304496290 |
| 15 | 1474567444350 |
| 16 | 23593081136625 |
| 17 | 401082379322625 |
| 18 | 7219482827807250 |
| 19 | 137170173728337750 |
| 20 | 2743403475221484075 |