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 | 0 |
| 2 | 1 |
| 3 | 4 |
| 4 | 31 |
| 5 | 288 |
| 6 | 3272 |
| 7 | 43580 |
| 8 | 666143 |
| 9 | 11491696 |
| 10 | 220875237 |
| 11 | 4681264432 |
| 12 | 108475235444 |
| 13 | 2728591657920 |
| 14 | 74051386322580 |
| 15 | 2156865088819692 |
| 16 | 67113404608820943 |
| 17 | 2221948578439255200 |
| 18 | 77990056655776149179 |