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 | 87 |
| 4 | 531 |
| 5 | 3333 |
| 6 | 21309 |
| 7 | 138015 |
| 8 | 902547 |
| 9 | 5946153 |
| 10 | 39406005 |
| 11 | 262404585 |
| 12 | 1754316045 |
| 13 | 11767931451 |
| 14 | 79165530375 |
| 15 | 533883963567 |
| 16 | 3608242091091 |
| 17 | 24432635451465 |
| 18 | 165721028062605 |
| 19 | 1125743155558677 |
| 20 | 7657535953619721 |
| 21 | 52151890274636463 |
| 22 | 355576809975214095 |