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 | 0 |
| 1 | 0 |
| 2 | 1 |
| 3 | 5 |
| 4 | 23 |
| 5 | 99 |
| 6 | 479 |
| 7 | 2645 |
| 8 | 19599 |
| 9 | 154007 |
| 10 | 1271519 |
| 11 | 11688489 |
| 12 | 126123095 |
| 13 | 1481833859 |
| 14 | 15162417087 |
| 15 | 126294191309 |
| 16 | 2497347563039 |
| 17 | 53642575418415 |
| 18 | 937621220224319 |
| 19 | 17116389710781136 |
| 20 | 281286727706878100 |