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 | -2 |
| 1 | 3 |
| 2 | 6 |
| 3 | 21 |
| 4 | 90 |
| 5 | 429 |
| 6 | 2184 |
| 7 | 11628 |
| 8 | 63954 |
| 9 | 360525 |
| 10 | 2072070 |
| 11 | 12096045 |
| 12 | 71524440 |
| 13 | 427496076 |
| 14 | 2578547760 |
| 15 | 15675792072 |
| 16 | 95951017602 |
| 17 | 590842763469 |
| 18 | 3657598059570 |
| 19 | 22749427475775 |
| 20 | 142096423925610 |
| 21 | 890949529108485 |
| 22 | 5605635937900320 |
| 23 | 35380499289211440 |
| 24 | 223951032734902200 |