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 | 21 |
| 3 | 117 |
| 4 | 497 |
| 5 | 2577 |
| 6 | 13937 |
| 7 | 72541 |
| 8 | 375054 |
| 9 | 1951949 |
| 10 | 10170792 |
| 11 | 52930039 |
| 12 | 275412159 |
| 13 | 1433386475 |
| 14 | 7460147264 |
| 15 | 38825258091 |
| 16 | 202060807970 |
| 17 | 1051605128451 |
| 18 | 5472968149750 |
| 19 | 28483454530439 |
| 20 | 148239012444720 |
| 21 | 771493812884305 |