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 | 6 |
| 2 | 30 |
| 3 | 150 |
| 4 | 750 |
| 5 | 3750 |
| 6 | 18735 |
| 7 | 93600 |
| 8 | 467640 |
| 9 | 2336400 |
| 10 | 11673000 |
| 11 | 58320000 |
| 12 | 291375210 |
| 13 | 1455753000 |
| 14 | 7273154040 |
| 15 | 36337737000 |
| 16 | 181548627000 |
| 17 | 907043385000 |
| 18 | 4531720872060 |
| 19 | 22641137570400 |
| 20 | 113118421225440 |
| 21 | 565156109349600 |