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 | 7 |
| 3 | 44 |
| 4 | 47 |
| 5 | 74 |
| 6 | 77 |
| 7 | 444 |
| 8 | 447 |
| 9 | 474 |
| 10 | 477 |
| 11 | 744 |
| 12 | 747 |
| 13 | 774 |
| 14 | 777 |
| 15 | 4444 |
| 16 | 4447 |
| 17 | 4474 |
| 18 | 4477 |
| 19 | 4744 |
| 20 | 4747 |
| 21 | 4774 |
| 22 | 4777 |
| 23 | 7444 |
| 24 | 7447 |
| 25 | 7474 |
| 26 | 7477 |
| 27 | 7744 |
| 28 | 7747 |
| 29 | 7774 |
| 30 | 7777 |
| 31 | 44444 |
| 32 | 44447 |
| 33 | 44474 |
| 34 | 44477 |
| 35 | 44744 |
| 36 | 44747 |
| 37 | 44774 |
| 38 | 44777 |
| 39 | 47444 |
| 40 | 47447 |
| 41 | 47474 |
| 42 | 47477 |
| 43 | 47744 |
| 44 | 47747 |