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 | 0 |
| 1 | 0 |
| 2 | 21 |
| 3 | 112 |
| 4 | 819 |
| 5 | 5712 |
| 6 | 39991 |
| 7 | 279936 |
| 8 | 1959552 |
| 9 | 13716864 |
| 10 | 96018048 |
| 11 | 672126336 |
| 12 | 4704884352 |
| 13 | 32934190464 |
| 14 | 230539333248 |
| 15 | 1613775332736 |
| 16 | 11296427329152 |
| 17 | 79074991304064 |
| 18 | 553524939128448 |
| 19 | 3874674573899136 |
| 20 | 27122722017293952 |