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 | 2 |
| 2 | 6 |
| 3 | 20 |
| 4 | 66 |
| 5 | 222 |
| 6 | 750 |
| 7 | 2536 |
| 8 | 8578 |
| 9 | 29018 |
| 10 | 98166 |
| 11 | 332092 |
| 12 | 1123458 |
| 13 | 3800630 |
| 14 | 12857438 |
| 15 | 43496400 |
| 16 | 147147266 |
| 17 | 497795634 |
| 18 | 1684030566 |
| 19 | 5697034596 |
| 20 | 19272929986 |
| 21 | 65199855118 |
| 22 | 220569529934 |
| 23 | 746181374904 |
| 24 | 2524313509762 |