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 | 5 |
| 2 | 10 |
| 3 | 70 |
| 4 | 310 |
| 5 | 1620 |
| 6 | 7790 |
| 7 | 39370 |
| 8 | 195300 |
| 9 | 978050 |
| 10 | 4882740 |
| 11 | 24421870 |
| 12 | 122069940 |
| 13 | 610390620 |
| 14 | 3051757490 |
| 15 | 15258982680 |
| 16 | 76293945000 |
| 17 | 381470703120 |
| 18 | 1907348623450 |
| 19 | 9536748046870 |
| 20 | 47683715818440 |