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 | 6 |
| 3 | 18 |
| 4 | 144 |
| 5 | 360 |
| 6 | 6480 |
| 7 | 15120 |
| 8 | 403200 |
| 9 | 2177280 |
| 10 | 32659200 |
| 11 | 119750400 |
| 12 | 8622028800 |
| 13 | 18681062400 |
| 14 | 784604620800 |
| 15 | 11769069312000 |
| 16 | 313841848320000 |
| 17 | 1067062284288000 |
| 18 | 115242726703104000 |
| 19 | 364935301226496000 |
| 20 | 43792236147179520000 |
| 21 | 459818479545384960000 |