 All about flooble | fun stuff | Get a free chatterbox | Free JavaScript | Avatars  perplexus dot info  Sum of 4 squares (Posted on 2018-07-08) The number N is a sum of 4 different numbers, each being a square of one of the 4 smallest divisors of N (e.g. N=36 does not qualify since 1^2+2^2+3^2+4^2
sums up to 30, not 36.)

Provide a full list of similar numbers or show that none exist.

 See The Solution Submitted by Ady TZIDON No Rating Comments: ( Back to comment list | You must be logged in to post comments.) Just S/W notes... Comment 4 of 4 | Two software notes:

Here is the Gnu Fortran version of the same routine for comparison.

Also, I worry about Charlie's cutoff of "sr=sqr(N)"

This would have missed, e.g., 3 as a factor of 6 (I think).

(I note this because I did the same thing at first.)

(Later... thinking it over, this makes sense since we can't use factors greater than sqrt(N) for the sum. Never mind!)

program dd

implicit none

integer list(4),i,j,k,jj,cnt

do 1 i=1,100000

cnt=0

do k=1,i

if(k*int((1.*i)/k).eq.i)then

cnt=cnt+1

list(cnt)=k

if(cnt.eq.4)then

jj=list(1)**2+list(2)**2+list(3)**2+list(4)**2

if(jj.eq.i)then

print*,' solved: ',i,list

go to 1

else

go to 1

endif

endif

endif

enddo

1           enddo

end

rabbit-3:~ lord\$ dd

solved:   130  1  2  5  10

Edited on July 9, 2018, 2:49 am

Edited on July 9, 2018, 6:21 pm
 Posted by Steven Lord on 2018-07-08 22:59:26 Please log in:

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