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 | 3 |
| 2 | 15 |
| 3 | 42 |
| 4 | 186 |
| 5 | 399 |
| 6 | 1680 |
| 7 | 3282 |
| 8 | 15876 |
| 9 | 31836 |
| 10 | 123690 |
| 11 | 277344 |
| 12 | 1541568 |
| 13 | 2391486 |
| 14 | 8992680 |
| 15 | 25483332 |
| 16 | 111757968 |
| 17 | 193819392 |
| 18 | 967814400 |
| 19 | 1744488660 |
| 20 | 9366647892 |
| 21 | 16912999320 |
| 22 | 62424587520 |
| 23 | 144219337920 |
| 24 | 852903426816 |
| 25 | 1397135488896 |
| 26 | 4766016364260 |
| 27 | 12477973754400 |