discrete mathematics - How to write psuedocode to compute n!!(double factorial) recursively? -

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n!!= 1*3*...*n, if n odd. n!!= 2*4*...*n, if n even.

i've been trying, i'm having tough time starting problem.

if n = 1, n!! = 1   if n = 2, n!! = 2   else n!! = n * (n-2)!!

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