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 | 4 |
| 2 | 15 |
| 3 | 76 |
| 4 | 373 |
| 5 | 2676 |
| 6 | 17539 |
| 7 | 152860 |
| 8 | 1383561 |
| 9 | 14658148 |
| 10 | 143131351 |
| 11 | 2070738924 |
| 12 | 24754959805 |
| 13 | 341745565396 |
| 14 | 5260157782923 |
| 15 | 92358395065276 |
| 16 | 1377499388715409 |
| 17 | 27622124789948100 |
| 18 | 476285499100204831 |
| 19 | 10464946811144407948 |
| 20 | 222724531608924013701 |