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 | 4 |
| 2 | 6 |
| 3 | 16 |
| 4 | 45 |
| 5 | 144 |
| 6 | 440 |
| 7 | 1440 |
| 8 | 4680 |
| 9 | 15600 |
| 10 | 52344 |
| 11 | 177840 |
| 12 | 608160 |
| 13 | 2095920 |
| 14 | 7262640 |
| 15 | 25300032 |
| 16 | 88517520 |
| 17 | 310927680 |
| 18 | 1095923400 |
| 19 | 3874804560 |
| 20 | 13737892896 |
| 21 | 48829153920 |
| 22 | 173949483240 |
| 23 | 620963048160 |
| 24 | 2220904271040 |
| 25 | 7956987570576 |
| 26 | 28553731537320 |
| 27 | 102617166646800 |