# A007757 (b-file synthesized from sequence entry)
1 1
2 2
3 36
4 144
5 1440
6 17280
7 241920
8 29030400
9 1567641600
10 156764160000
11 217275125760000
12 1738201006080000
13 45193226158080000
14 3796230997278720000
15 113886929918361600000
16 1822190878693785600000
17 22489479824838701875200000
18 28336744579296764362752000000
19 1076796294013277045784576000000
20 1679802218660712191423938560000000