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 | 1 |
| 1 | 1 |
| 2 | 4 |
| 3 | 18 |
| 4 | 106 |
| 5 | 750 |
| 6 | 6188 |
| 7 | 58184 |
| 8 | 613156 |
| 9 | 7149780 |
| 10 | 91319712 |
| 11 | 1267089912 |
| 12 | 18969355656 |
| 13 | 304646227704 |
| 14 | 5222700792528 |
| 15 | 95169251327040 |
| 16 | 1836450816902928 |
| 17 | 37403582826055824 |
| 18 | 801728489886598848 |
| 19 | 18037821249349491360 |
| 20 | 424970923585819603872 |
| 21 | 10462258547232790348512 |