The sum of all natural numbers n such that 100<n<200 and gcd(91,n)>1 is:
Solutions · 1
Official solution
91=7×13; the required numbers are those divisible by 7 or 13.
Sum divisible by 7 (105 to 196): 2107. Sum divisible by 13 (104 to 195): 1196. Sum divisible by 91: 182.
2107+1196−182=3121.