A222475 - OEIS

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A222475 as a simple table

n	a(n)
1	4
2	10
3	42
4	235
5	1450
6	30883
7	267772
8	7073732
9	67911068
10	1835377464
11	17762404598
12	478005487727
13	4694125854134
14	124576004895424
15	1240340640828968
16	32486189811716076
17	327738319146833494
18	8473377832221877331

[4,10,42,235,1450,30883,267772,7073732,67911068, 1835377464,17762404598,478005487727,4694125854134, 124576004895424,1240340640828968, 32486189811716076,327738319146833494, 8473377832221877331]