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 | 20 |
| 4 | 110 |
| 5 | 670 |
| 6 | 4470 |
| 7 | 32440 |
| 8 | 254490 |
| 9 | 2146525 |
| 10 | 19374399 |
| 11 | 186356108 |
| 12 | 1903188611 |
| 13 | 20569046543 |
| 14 | 234562076984 |
| 15 | 2814847291152 |
| 16 | 35461339995304 |
| 17 | 467952904377739 |
| 18 | 6455368497736153 |
| 19 | 92919917495585794 |
| 20 | 1393239845937756837 |
| 21 | 21726457354762648604 |