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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 9 |
| 3 | 20 |
| 4 | 51 |
| 5 | 136 |
| 6 | 414 |
| 7 | 1300 |
| 8 | 4371 |
| 9 | 15084 |
| 10 | 53508 |
| 11 | 192700 |
| 12 | 703346 |
| 13 | 2589304 |
| 14 | 9603954 |
| 15 | 35824240 |
| 16 | 134285331 |
| 17 | 505421344 |
| 18 | 1909144014 |
| 19 | 7234153420 |
| 20 | 27488865564 |
| 21 | 104717491064 |
| 22 | 399826699734 |
| 23 | 1529763696820 |
| 24 | 5864079144466 |
| 25 | 22518031691368 |
| 26 | 86607753541164 |
[1,4,9,20,51,136,414,1300,4371,15084,53508,192700, 703346,2589304,9603954,35824240,134285331, 505421344,1909144014,7234153420,27488865564, 104717491064,399826699734,1529763696820, 5864079144466,22518031691368,86607753541164] |