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 | 2 |
| 3 | 21 |
| 4 | 220 |
| 5 | 3545 |
| 6 | 70566 |
| 7 | 1702267 |
| 8 | 48438104 |
| 9 | 1582227873 |
| 10 | 58475787850 |
| 11 | 2410935939731 |
| 12 | 109728296017572 |
| 13 | 5464423604085745 |
| 14 | 295562179335075758 |
| 15 | 17255009243888243115 |
| 16 | 1081438061864539992496 |
| 17 | 72422934220506772042817 |
| 18 | 5161269584065131270532242 |