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 | 1 |
| 3 | 3 |
| 4 | 20 |
| 5 | 132 |
| 6 | 1888 |
| 7 | 20128 |
| 8 | 584000 |
| 9 | 17102016 |
| 10 | 553895936 |
| 11 | 11616690176 |
| 12 | 743337949184 |
| 13 | 19467186157568 |
| 14 | 999551845713920 |
| 15 | 66437400489711616 |
| 16 | 10253161206302064640 |
| 17 | 388089999627661557760 |
| 18 | 53727789519052432998400 |
| 19 | 2325767421950553303285760 |
| 20 | 365546030278816140131041280 |