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 | 0 |
| 3 | 1 |
| 4 | 13 |
| 5 | 90 |
| 6 | 656 |
| 7 | 4862 |
| 8 | 39938 |
| 9 | 362122 |
| 10 | 3627433 |
| 11 | 39913180 |
| 12 | 478994407 |
| 13 | 6227001093 |
| 14 | 87178250333 |
| 15 | 1307674292294 |
| 16 | 20922789757983 |
| 17 | 355687427756494 |
| 18 | 6402373705060610 |
| 19 | 121645100407007344 |
| 20 | 2432902008172915083 |
| 21 | 51090942171702654311 |
| 22 | 1124000727777596134102 |
| 23 | 25852016738884946540910 |
| 24 | 620448401733239380526706 |
| 25 | 15511210043330985878651420 |