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 | 0 |
| 1 | 0 |
| 2 | 2 |
| 3 | 2 |
| 4 | 8 |
| 5 | 20 |
| 6 | 60 |
| 7 | 212 |
| 8 | 632 |
| 9 | 2508 |
| 10 | 8280 |
| 11 | 34256 |
| 12 | 127712 |
| 13 | 542984 |
| 14 | 2252432 |
| 15 | 9873216 |
| 16 | 44557424 |
| 17 | 202661012 |
| 18 | 975470880 |
| 19 | 4627469192 |
| 20 | 23413518704 |
| 21 | 116147688600 |
| 22 | 611882489152 |
| 23 | 3174544514192 |
| 24 | 17312022302368 |
| 25 | 93772475206800 |
| 26 | 527582381206400 |
| 27 | 2975078868145952 |