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 | 0 |
| 1 | 5 |
| 2 | 20 |
| 3 | 80 |
| 4 | 380 |
| 5 | 1820 |
| 6 | 9020 |
| 7 | 44720 |
| 8 | 223220 |
| 9 | 1114280 |
| 10 | 5569580 |
| 11 | 27838880 |
| 12 | 139185380 |
| 13 | 695882180 |
| 14 | 3479366180 |
| 15 | 17396607680 |
| 16 | 86982815180 |
| 17 | 434912961620 |
| 18 | 2174563693820 |
| 19 | 10872812899520 |
| 20 | 54364058928020 |
| 21 | 271820266801220 |
| 22 | 1359101306167220 |
| 23 | 6795506391650720 |