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 | 1 |
| 2 | 1 |
| 3 | 4 |
| 4 | 25 |
| 5 | 220 |
| 6 | 2485 |
| 7 | 34300 |
| 8 | 559405 |
| 9 | 10525900 |
| 10 | 224449225 |
| 11 | 5348843500 |
| 12 | 140880765025 |
| 13 | 4063875715900 |
| 14 | 127418482316125 |
| 15 | 4314607214417500 |
| 16 | 156920190449147125 |
| 17 | 6100643259005795500 |
| 18 | 252476539015516440625 |
| 19 | 11081983532721088487500 |
| 20 | 514215436341672155715625 |