A273688 - OEIS

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A273688 as a simple table

n	a(n)
0	1
1	5
2	17
3	49
4	261
5	1081
6	3993
7	15521
8	61921
9	248613
10	997825
11	3981665
12	15954309
13	63723117
14	255045061
15	1019793809

[1,5,17,49,261,1081,3993,15521,61921,248613, 997825,3981665,15954309,63723117,255045061, 1019793809]