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 | 3 |
| 2 | 15 |
| 3 | 111 |
| 4 | 1095 |
| 5 | 13503 |
| 6 | 199815 |
| 7 | 3449631 |
| 8 | 68062695 |
| 9 | 1510769343 |
| 10 | 37260156615 |
| 11 | 1010843385951 |
| 12 | 29916558512295 |
| 13 | 959183053936383 |
| 14 | 33118910817665415 |
| 15 | 1225219266296167071 |
| 16 | 48348200298184769895 |
| 17 | 2027102674516399522623 |
| 18 | 89990106205541777926215 |
| 19 | 4216915299772659459872991 |