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 | 3 |
| 1 | 15 |
| 2 | 99 |
| 3 | 687 |
| 4 | 4803 |
| 5 | 33615 |
| 6 | 235299 |
| 7 | 1647087 |
| 8 | 11529603 |
| 9 | 80707215 |
| 10 | 564950499 |
| 11 | 3954653487 |
| 12 | 27682574403 |
| 13 | 193778020815 |
| 14 | 1356446145699 |
| 15 | 9495123019887 |
| 16 | 66465861139203 |
| 17 | 465261027974415 |
| 18 | 3256827195820899 |
| 19 | 22797790370746287 |