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Albert Chan · 09-09-2021, 03:33 PM

(09-09-2021 07:24 AM)Werner Wrote:
(09-07-2021 02:21 PM)Albert Chan Wrote:

Code:

def subfac(n, r=0): # integer n > 0 for i in range(2,n+1): r = 1-i*r return abs(r)

Shouldn't that be
for i in range (2,n) ?

No, Python use 0-based indexing, open-intervals. To loop from 2 to n, we need range(2, n+1)

Mathematica have Subfactorial[n], but DIY is trivial, just nest (n+1) - 2 = n-1 times:

In[1]:= subfac[n_] := Nest[{1+First[#], 1-Times@@#}&, {2,0}, n-1] // Last // Abs

In[2]:= subfac[30]
Out[2]= 97581073836835777732377428235481

In[3]:= Round[30!/E]
Out[3]= 97581073836835777732377428235481