A337520 - OEIS

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A337520 as a simple table

n	a(n)
0	1
1	1
2	2
3	4
4	10
5	22
6	64
7	147
8	409
9	1092
10	3253
11	8661
12	28585
13	83190
14	274001
15	912373
16	3366384
17	13253582
18	61533277
19	290493694

[1,1,2,4,10,22,64,147,409,1092,3253,8661,28585, 83190,274001,912373,3366384,13253582,61533277, 290493694]