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A180239
as a simple table
n
a(n)
0
1
1
4
2
16
3
64
4
244
5
856
6
2776
7
8356
8
23032
9
59200
10
142624
11
324484
12
696256
13
1422436
14
2779900
15
5219452
16
9455596
[1,4,16,64,244,856,2776,8356,23032,59200,142624, 324484,696256,1422436,2779900,5219452,9455596]