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 | 1 |
| 2 | 7 |
| 3 | 55 |
| 4 | 505 |
| 5 | 5497 |
| 6 | 69823 |
| 7 | 1007407 |
| 8 | 16157905 |
| 9 | 284214097 |
| 10 | 5432922775 |
| 11 | 112034017735 |
| 12 | 2476196276617 |
| 13 | 58332035387017 |
| 14 | 1457666574447247 |
| 15 | 38485034941511935 |
| 16 | 1069787864231083297 |
| 17 | 31213730550761076769 |
| 18 | 953352927192964243879 |
| 19 | 30406448846308128741847 |