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) |
|---|---|
| 1 | 0 |
| 2 | 1023 |
| 3 | 59048 |
| 4 | 1048575 |
| 5 | 9765624 |
| 6 | 60466175 |
| 7 | 282475248 |
| 8 | 1073741823 |
| 9 | 3486784400 |
| 10 | 9999999999 |
| 11 | 25937424600 |
| 12 | 61917364223 |
| 13 | 137858491848 |
| 14 | 289254654975 |
| 15 | 576650390624 |
| 16 | 1099511627775 |
| 17 | 2015993900448 |
| 18 | 3570467226623 |
| 19 | 6131066257800 |
| 20 | 10239999999999 |
| 21 | 16679880978200 |