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 | 3 |
| 3 | 15 |
| 4 | 103 |
| 5 | 879 |
| 6 | 8799 |
| 7 | 99711 |
| 8 | 1250175 |
| 9 | 17077215 |
| 10 | 251414175 |
| 11 | 3958086015 |
| 12 | 66245028447 |
| 13 | 1173340901695 |
| 14 | 21914481618591 |
| 15 | 430320455540223 |
| 16 | 8861927054203743 |
| 17 | 190989549802914495 |
| 18 | 4299479144808402975 |
| 19 | 100927457271249951615 |
| 20 | 2466702562122306371295 |
| 21 | 62678175995432599506495 |