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 | 4 |
| 2 | 20 |
| 3 | 76 |
| 4 | 260 |
| 5 | 840 |
| 6 | 2616 |
| 7 | 7940 |
| 8 | 23644 |
| 9 | 69380 |
| 10 | 201220 |
| 11 | 578064 |
| 12 | 1647600 |
| 13 | 4664836 |
| 14 | 13132580 |
| 15 | 36789820 |
| 16 | 102621956 |
| 17 | 285174360 |
| 18 | 789810984 |
| 19 | 2180889860 |
| 20 | 6005842540 |
| 21 | 16498958324 |
| 22 | 45225010180 |
| 23 | 123715684896 |
| 24 | 337806904800 |
| 25 | 920819997700 |