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) |
|---|---|
| 1 | 0 |
| 2 | 1 |
| 3 | 3 |
| 4 | 13 |
| 5 | 71 |
| 6 | 463 |
| 7 | 3497 |
| 8 | 29975 |
| 9 | 287265 |
| 10 | 3042545 |
| 11 | 35284315 |
| 12 | 444617525 |
| 13 | 6048575335 |
| 14 | 88347242335 |
| 15 | 1378930649745 |
| 16 | 22903345844335 |
| 17 | 403342641729665 |
| 18 | 7506843094993825 |
| 19 | 147226845692229875 |
| 20 | 3034786640911840925 |
| 21 | 65592491119118514375 |