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 | 4 |
| 2 | 21 |
| 3 | 116 |
| 4 | 609 |
| 5 | 3100 |
| 6 | 15589 |
| 7 | 78076 |
| 8 | 390561 |
| 9 | 1953044 |
| 10 | 9765525 |
| 11 | 48828004 |
| 12 | 244140481 |
| 13 | 1220702956 |
| 14 | 6103515429 |
| 15 | 30517577900 |
| 16 | 152587890369 |
| 17 | 762939452836 |
| 18 | 3814697265301 |
| 19 | 19073486327764 |
| 20 | 95367431640225 |