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Factorials and 2 powers (Posted on 2021-08-13) Difficulty: 3 of 5
Find all pairs (k,n) of positive integers such that

k!=(2n-1)(2n-2)(2n-4)...(2n-2n-1)

No Solution Yet Submitted by Danish Ahmed Khan    
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Some Thoughts computer findings | Comment 1 of 5
clearvars, clc
digits(5000)
f=vpa(1); nxtno=2;
for n=1:11
   rhs=p2(n); 
   disp([n rhs]) 
   while f<rhs
      f=f*nxtno; nxtno=nxtno+1;
   end
   if rhs==f
      disp(f) 
   end
end

function pr = p2(n)
 
  p0=vpa(2)^vpa(n);
  p=vpa(1);
  for i=p0-1:-1:p0-p0/2
     p=p*vpa(i); 
  end
  pr=p;
end

finds only n=1 and n=2, where the respective equal values are 1 and 6. The limit of testing was n=11 as beyond that the RHS becomes larger than the allotted 5000 digits (the program keeps building the factorial until it equals or exceeds the RHS).

Oh, yes, forgot: the k values are 1 and 3 respectively.

Edited on August 13, 2021, 10:35 am
  Posted by Charlie on 2021-08-13 09:22:08

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