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 | 4 |
| 3 | 22 |
| 4 | 112 |
| 5 | 580 |
| 6 | 2992 |
| 7 | 15448 |
| 8 | 79744 |
| 9 | 411664 |
| 10 | 2125120 |
| 11 | 10970464 |
| 12 | 56632576 |
| 13 | 292353088 |
| 14 | 1509207808 |
| 15 | 7790949760 |
| 16 | 40219045888 |
| 17 | 207621882112 |
| 18 | 1071801803776 |
| 19 | 5532938507776 |
| 20 | 28562564853760 |