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 | 5 |
| 3 | 20 |
| 4 | 105 |
| 5 | 644 |
| 6 | 4585 |
| 7 | 37134 |
| 8 | 337393 |
| 9 | 3399416 |
| 10 | 37622961 |
| 11 | 453769370 |
| 12 | 5924234041 |
| 13 | 83242063332 |
| 14 | 1252567177849 |
| 15 | 20096182035734 |
| 16 | 342461702459745 |
| 17 | 6177536369911664 |
| 18 | 117598028364137953 |
| 19 | 2356007639327453106 |
| 20 | 49553054794725702121 |
| 21 | 1091705092860949184540 |