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A121639 as a simple table

na(n)
10
21
35
425
5147
6996
77668
866264
9635976
106717600
1177482080
12969338880
1313076778240
14189261999360
152925629280000
1648111515827200
17838731380659200
1815451544605593600
19299960798422118400
206120505381423104000

[0,1,5,25,147,996,7668,66264,635976,6717600,
 77482080,969338880,13076778240,189261999360,
 2925629280000,48111515827200,838731380659200,
 15451544605593600,299960798422118400,
 6120505381423104000]