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 | 124 |
| 4 | 773 |
| 5 | 4988 |
| 6 | 33029 |
| 7 | 223228 |
| 8 | 1533957 |
| 9 | 10686460 |
| 10 | 75309061 |
| 11 | 535920636 |
| 12 | 3845881861 |
| 13 | 27800469500 |
| 14 | 202244161541 |
| 15 | 1479594737660 |
| 16 | 10878806654981 |
| 17 | 80345708888060 |
| 18 | 595788935725061 |
| 19 | 4434080431079420 |
| 20 | 33109442115403781 |