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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 18 |
| 3 | 84 |
| 4 | 400 |
| 5 | 1928 |
| 6 | 9368 |
| 7 | 45776 |
| 8 | 224608 |
| 9 | 1105536 |
| 10 | 5454784 |
| 11 | 26966272 |
| 12 | 133518464 |
| 13 | 661936512 |
| 14 | 3285120384 |
| 15 | 16318182656 |
| 16 | 81118238208 |
| 17 | 403499984896 |
| 18 | 2008203312128 |
| 19 | 9999508994048 |
| 20 | 49811499909120 |
| 21 | 248220669087744 |
| 22 | 1237327213948928 |
| 23 | 6169546670055424 |
| 24 | 30770185224601600 |
| 25 | 153498159158099968 |
[1,4,18,84,400,1928,9368,45776,224608,1105536, 5454784,26966272,133518464,661936512,3285120384, 16318182656,81118238208,403499984896, 2008203312128,9999508994048,49811499909120, 248220669087744,1237327213948928,6169546670055424, 30770185224601600,153498159158099968] |