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Some 2 Powers Sum to Factorial (Posted on 2023-02-27) Difficulty: 3 of 5
Determine all possible triplets (p, q, n) of nonnegative integers that satisfy this equation:
                 2p + 2q = n! 
Provide valid argument for your answer.

*** Adapted from a problem which appeared at the Harvard/MIT math Olympiad.

See The Solution Submitted by K Sengupta    
Rating: 5.0000 (1 votes)

Comments: ( Back to comment list | You must be logged in to post comments.)
re: without proof of completeness | Comment 2 of 5 |
(In reply to without proof of completeness by Charlie)

https://oeis.org/A079584


There is a solution if and only if n>1 and the number of ones in the binary representation of n! is either 1 or 2.  

The link has a table that shows there are no solutions (beyond n=2, 3, or 4) below 10,000.  The sequence grows quickly, though not monotonically.  It's pretty darn clear though that there will not be any solutions beyond 10,000.  



  Posted by Jer on 2023-02-27 14:00:54
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