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 | 4 |
| 2 | 15 |
| 3 | 52 |
| 4 | 240 |
| 5 | 1121 |
| 6 | 4888 |
| 7 | 20047 |
| 8 | 77280 |
| 9 | 277441 |
| 10 | 1093425 |
| 11 | 5279468 |
| 12 | 23647519 |
| 13 | 99429196 |
| 14 | 393425745 |
| 15 | 1457109628 |
| 16 | 4968639359 |
| 17 | 24553864319 |
| 18 | 113193708472 |
| 19 | 488133974353 |
| 20 | 1980778750800 |
| 21 | 7547952442399 |
| 22 | 26710380775592 |
| 23 | 112605054449252 |