20120610, 17:40  #34 
"Forget I exist"
Jul 2009
Dartmouth NS
20E2_{16} Posts 
okay it's not as good as I thought but I can explain it using sets:
basically when trying to find (sigma(x*y)x*y) using (sigma(x)x) it depends on sigma(y) and the intersection of 2*divsors(x) and divisors(x): 6=[1,2,3,6] for y = 2 adds on to [2,4,6,12] which have intersection [2,6] 3*(sigma(6)6) +6  (2+6) = 248 = 16 since odd numbers don't have even divisors this problem for y=2 only shows up in even number x , other y may create problems in the odd numbered x. 12=[1,2,3,4,6,12] Code:
sigma2(n,d)=sum(x=1,#divisors(n),sigma(d)*divisors(n)[x])sum(y=1,#intersection(divisors(n),divisors(n)*d),intersection(divisors(n),divisors(n)*d)[y])d*n Code:
intersection(x,y,pretty)=C=[];for(i=1,#x,for(j=1,#y,if(x[i]==y[j],C=concat(C,x[i]))));if(pretty!=0,printVectorAsSet(vecsort(C,,8)),vecsort(C,,8)) Last fiddled with by science_man_88 on 20120610 at 18:24 
20120610, 21:53  #35  
"Forget I exist"
Jul 2009
Dartmouth NS
10000011100010_{2} Posts 
Quote:


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