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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 16 |
| 3 | 60 |
| 4 | 215 |
| 5 | 747 |
| 6 | 2539 |
| 7 | 8491 |
| 8 | 28049 |
| 9 | 91782 |
| 10 | 298109 |
| 11 | 962594 |
| 12 | 3093687 |
| 13 | 9905444 |
| 14 | 31619072 |
| 15 | 100681587 |
| 16 | 319944693 |
| 17 | 1015039586 |
| 18 | 3215903436 |
| 19 | 10177462312 |
| 20 | 32179381609 |
| 21 | 101668695088 |
| 22 | 321014982282 |
| 23 | 1013068488800 |
| 24 | 3195703133266 |
| 25 | 10077204123667 |
| 26 | 31767718475161 |
[1,4,16,60,215,747,2539,8491,28049,91782,298109, 962594,3093687,9905444,31619072,100681587, 319944693,1015039586,3215903436,10177462312, 32179381609,101668695088,321014982282, 1013068488800,3195703133266,10077204123667, 31767718475161] |