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A366671
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Smallest prime dividing 8^n + 1.
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5
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2, 3, 5, 3, 17, 3, 5, 3, 97, 3, 5, 3, 17, 3, 5, 3, 193, 3, 5, 3, 17, 3, 5, 3, 97, 3, 5, 3, 17, 3, 5, 3, 641, 3, 5, 3, 17, 3, 5, 3, 97, 3, 5, 3, 17, 3, 5, 3, 193, 3, 5, 3, 17, 3, 5, 3, 97, 3, 5, 3, 17, 3, 5, 3, 769, 3, 5, 3, 17, 3, 5, 3, 97, 3, 5, 3, 17, 3, 5
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OFFSET
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0,1
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COMMENTS
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a(n) = 3 if n is odd. a(n) = 5 if n == 2 (mod 4). - Robert Israel, Nov 20 2023
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LINKS
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FORMULA
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MAPLE
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P1000:= mul(ithprime(i), i= 4..1000):
f:= proc(n) local t;
if n::odd then return 3 elif n mod 4 = 2 then return 5 fi;
t:= igcd(8^n+1, P1000);
if t <> 1 then min(numtheory:-factorset(t)) else min(numtheory:-factorset(8^n+1)) fi
end proc:
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MATHEMATICA
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PROG
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(Python)
from sympy import primefactors
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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