Wednesday, 1 August 2018

divisibility - When an integer is disible by 17,19,23, or 41?

Let n=am10m++am110m1++a2102+a110+a0 where ak are integers and 0ak9,k=0,1,,m be the decimal representation of a positive integer n.
Let S=a0+a1++am,T=a0a1++(1)mam. Then
1.n is divisible by 2 iff a_0 is divisible by 2.
2. n is divisible by 11 iff T is divisible by 11.
3. n is divisible by 3 iff S is divisible by 3.
I know the proof of these results. I shall prove first one and the proof of rest two are similar.
Now my question : Is there any similar rule which will tell us whether an integer
n is divisible by the primes 17,19,23,37,41 etc or not?

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