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 | 28 |
| 3 | 248 |
| 4 | 2480 |
| 5 | 26688 |
| 6 | 301648 |
| 7 | 3531424 |
| 8 | 42449088 |
| 9 | 520858496 |
| 10 | 6497190528 |
| 11 | 82146802944 |
| 12 | 1050370074624 |
| 13 | 13559126110720 |
| 14 | 176469550681344 |
| 15 | 2313050095245824 |
| 16 | 30506619439926272 |
| 17 | 404558181197010944 |
| 18 | 5391161355764205568 |
| 19 | 72156618656648237056 |
| 20 | 969557980700415827968 |