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 | 0 |
| 2 | 2 |
| 3 | 18 |
| 4 | 116 |
| 5 | 650 |
| 6 | 3372 |
| 7 | 16660 |
| 8 | 79592 |
| 9 | 371034 |
| 10 | 1697660 |
| 11 | 7654460 |
| 12 | 34106712 |
| 13 | 150499908 |
| 14 | 658707896 |
| 15 | 2863150440 |
| 16 | 12371226064 |
| 17 | 53178791162 |
| 18 | 227561427612 |
| 19 | 969890051884 |
| 20 | 4119092850680 |
| 21 | 17438036501676 |
| 22 | 73611934643368 |
| 23 | 309935825654168 |
| 24 | 1301878616066736 |