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 | 7 |
| 2 | 63 |
| 3 | 504 |
| 4 | 4088 |
| 5 | 32697 |
| 6 | 262080 |
| 7 | 2096577 |
| 8 | 16776648 |
| 9 | 134213128 |
| 10 | 1073737224 |
| 11 | 8589897288 |
| 12 | 68719439943 |
| 13 | 549755515008 |
| 14 | 4398046212672 |
| 15 | 35184369697407 |
| 16 | 281474974319672 |
| 17 | 2251799794521144 |
| 18 | 18014398490350584 |
| 19 | 144115187922510840 |
| 20 | 1152921504453534648 |