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 | 89 |
| 4 | 580 |
| 5 | 4009 |
| 6 | 28857 |
| 7 | 213967 |
| 8 | 1622869 |
| 9 | 12531090 |
| 10 | 98171544 |
| 11 | 778364379 |
| 12 | 6233789872 |
| 13 | 50355710215 |
| 14 | 409790010350 |
| 15 | 3356429972859 |
| 16 | 27647745771339 |
| 17 | 228890532343859 |
| 18 | 1903475080613014 |
| 19 | 15893483726218904 |
| 20 | 133190665385526309 |
| 21 | 1119863488613216952 |