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 | 8 |
| 4 | 46 |
| 5 | 324 |
| 6 | 2708 |
| 7 | 26424 |
| 8 | 295272 |
| 9 | 3714600 |
| 10 | 51929472 |
| 11 | 798610416 |
| 12 | 13399081584 |
| 13 | 243556758912 |
| 14 | 4767863027328 |
| 15 | 100004300847744 |
| 16 | 2237419620187776 |
| 17 | 53187370914349440 |
| 18 | 1338737435337261312 |
| 19 | 35568441673932566016 |
| 20 | 994744655047298951424 |
| 21 | 29211127285363209561600 |