Tessellate S.T.E.M.S. (2019) - Mathematics - Category A (School) - Set 5 - Objective Problem 3

Find the total number of pairs of positive integer primes ( p , q ) (p,q) such that ( 3 p q 1 + 1 ) ( 1 1 p + 1 7 p ) (3p^{q-1}+1)|(11^p+17^p) .


This problem is a part of Tessellate S.T.E.M.S. (2019)
more than 3 3 2 2 1 1 3 3

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1 solution

I Really do not understand which primes satisfy the condition.

If p = 2 p=2 , then 3. 2 q 1 + 1 1 1 2 + 7 2 = 170 3.2^{q-1}+1 | 11^2+7^2=170 . Therefore q 6 q \leq 6 and for non of such q q the condition is satisfied.

If p 2 p \neq 2 , then p p is odd and 1 1 p + 7 p = ( 11 + 7 ) ( 1 1 p 1 1 1 p 2 . 7 + 1 1 p 3 . 7 + 7 p 1 ) 11^p+7^p=(11+7)(11^{p-1}-11^{p-2}.7+11^{p-3}.7- \dots +7^{p-1} ) . So, 4 1 1 p + 7 p 4 \nmid 11^p+7^p . But, if q q is odd then 4 3. p q 1 + 1 4 | 3.p^{q-1}+1 , because (knowing Euler theorem)

3. p q 1 1. ( p 2 ) k 1 m o d 4 3.p^{q-1}\equiv -1.(p^{2})^k \equiv -1 \ mod 4

So, for no prime pair ( p , q ) (p,q) the condition is satisfied.

Apologies, there was a typo in the problem. Thanks for pointing out the error.

Cheers,

Tessellate S.T.E.M.S. Math community

Tessellate S.T.E.M.S. Mathematics - 2 years, 5 months ago

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