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 | 3 |
| 2 | 20 |
| 3 | 102 |
| 4 | 565 |
| 5 | 3042 |
| 6 | 16538 |
| 7 | 89610 |
| 8 | 486103 |
| 9 | 2635899 |
| 10 | 14295131 |
| 11 | 77522409 |
| 12 | 420410296 |
| 13 | 2279906481 |
| 14 | 12364072580 |
| 15 | 67051079697 |
| 16 | 363621959233 |
| 17 | 1971943176024 |
| 18 | 10693963589630 |
| 19 | 57993991716273 |
| 20 | 314504819239756 |
| 21 | 1705578083028348 |