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) |
|---|---|
| 1 | 1 |
| 2 | 5 |
| 3 | 25 |
| 4 | 143 |
| 5 | 942 |
| 6 | 7074 |
| 7 | 59832 |
| 8 | 563688 |
| 9 | 5858640 |
| 10 | 66622320 |
| 11 | 823055040 |
| 12 | 10979133120 |
| 13 | 157300375680 |
| 14 | 2409321801600 |
| 15 | 39290164300800 |
| 16 | 679701862425600 |
| 17 | 12433400027596800 |
| 18 | 239791474805299200 |
| 19 | 4863054420016128000 |
| 20 | 103462238924835840000 |
| 21 | 2304147629440419840000 |