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 | 4 |
| 1 | 24 |
| 2 | 132 |
| 3 | 672 |
| 4 | 3192 |
| 5 | 15996 |
| 6 | 74396 |
| 7 | 354936 |
| 8 | 1639764 |
| 9 | 7669876 |
| 10 | 35282064 |
| 11 | 162809928 |
| 12 | 745459776 |
| 13 | 3413032716 |
| 14 | 15560103924 |
| 15 | 70861321612 |
| 16 | 321879751956 |
| 17 | 1460223461700 |
| 18 | 6612700085376 |
| 19 | 29909912167920 |