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 | 4 |
| 2 | 20 |
| 3 | 108 |
| 4 | 544 |
| 5 | 2540 |
| 6 | 11544 |
| 7 | 52192 |
| 8 | 231872 |
| 9 | 1014444 |
| 10 | 4401400 |
| 11 | 19016888 |
| 12 | 81588720 |
| 13 | 347833408 |
| 14 | 1476460496 |
| 15 | 6250982640 |
| 16 | 26366866432 |
| 17 | 110825294252 |
| 18 | 464575219704 |
| 19 | 1944165731800 |
| 20 | 8117172816560 |
| 21 | 33813868882584 |
| 22 | 140605002878032 |
| 23 | 583960731640688 |
| 24 | 2421457649730528 |
| 25 | 10025040350809600 |