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 | 1 |
| 2 | 3 |
| 3 | 15 |
| 4 | 60 |
| 5 | 255 |
| 6 | 1005 |
| 7 | 4095 |
| 8 | 16320 |
| 9 | 65520 |
| 10 | 261885 |
| 11 | 1048575 |
| 12 | 4193220 |
| 13 | 16777215 |
| 14 | 67104765 |
| 15 | 268435185 |
| 16 | 1073725440 |
| 17 | 4294967295 |
| 18 | 17179802640 |
| 19 | 68719476735 |
| 20 | 274877644740 |
| 21 | 1099511623665 |
| 22 | 4398045462525 |
| 23 | 17592186044415 |
| 24 | 70368739967040 |
| 25 | 281474976710400 |