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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 13 |
| 3 | 47 |
| 4 | 188 |
| 5 | 825 |
| 6 | 3937 |
| 7 | 20270 |
| 8 | 111835 |
| 9 | 657423 |
| 10 | 4097622 |
| 11 | 26965867 |
| 12 | 186685725 |
| 13 | 1355314108 |
| 14 | 10289242825 |
| 15 | 81481911259 |
| 16 | 671596664012 |
| 17 | 5749877335253 |
| 18 | 51042081429213 |
| 19 | 469037073951694 |
| 20 | 4454991580211951 |
| 21 | 43677136038927595 |
| 22 | 441452153556357966 |
| 23 | 4594438326374915007 |
[1,4,13,47,188,825,3937,20270,111835,657423, 4097622,26965867,186685725,1355314108,10289242825, 81481911259,671596664012,5749877335253, 51042081429213,469037073951694,4454991580211951, 43677136038927595,441452153556357966, 4594438326374915007] |