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A000138 as a simple table

na(n)
01
11
22
36
418
590
6540
73780
831500
9283500
102835000
1131185000
12372972600
134848643800
1467881013200
151018215198000
1616294848570000
17277012425690000
184986223662420000
1994738249585980000
201894745192712372000
2139789649046959812000
22875372279033115864000

[1,1,2,6,18,90,540,3780,31500,283500,2835000,
 31185000,372972600,4848643800,67881013200,
 1018215198000,16294848570000,277012425690000,
 4986223662420000,94738249585980000,
 1894745192712372000,39789649046959812000,
 875372279033115864000]