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 | 2 |
| 1 | 20 |
| 2 | 210 |
| 3 | 2352 |
| 4 | 27720 |
| 5 | 339768 |
| 6 | 4294290 |
| 7 | 55621280 |
| 8 | 734959368 |
| 9 | 9873696560 |
| 10 | 134510127752 |
| 11 | 1854385377600 |
| 12 | 25828939188000 |
| 13 | 362995937665200 |
| 14 | 5141806953167250 |
| 15 | 73343003232628800 |
| 16 | 1052697272275341000 |
| 17 | 15194039267330154000 |
| 18 | 220410039466873456200 |