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 | 9 |
| 3 | 68 |
| 4 | 552 |
| 5 | 4524 |
| 6 | 37531 |
| 7 | 314280 |
| 8 | 2651418 |
| 9 | 22503384 |
| 10 | 191935926 |
| 11 | 1643789136 |
| 12 | 14126691568 |
| 13 | 121764645876 |
| 14 | 1052237509089 |
| 15 | 9113317001712 |
| 16 | 79084764081720 |
| 17 | 687489330917088 |
| 18 | 5985694255080435 |
| 19 | 52187865620386860 |
| 20 | 455587704842911596 |