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 | 126 |
| 4 | 797 |
| 5 | 5190 |
| 6 | 34439 |
| 7 | 231556 |
| 8 | 1572135 |
| 9 | 10754148 |
| 10 | 74001735 |
| 11 | 511686726 |
| 12 | 3552251429 |
| 13 | 24743806370 |
| 14 | 172853699427 |
| 15 | 1210514603212 |
| 16 | 8495774193707 |
| 17 | 59739915525288 |
| 18 | 420785972800187 |
| 19 | 2968344133842182 |
| 20 | 20967995689677183 |