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A216185
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a(n) is the smallest odd number k with GCD(k,n)=1 such that all the powers of 2 mod k are distinct from n mod k, or 0 if n is a power of 2.
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1
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0, 7, 0, 7, 7, 15, 0, 31, 7, 15, 7, 7, 15, 23, 0, 7, 31, 7, 7, 23, 15, 17, 7, 31, 7, 7, 15, 15, 23, 7, 0, 7, 7, 39, 31, 15, 7, 17, 7, 7, 23, 15, 15, 7, 17, 7, 7, 31, 31, 23, 7, 23, 7, 7, 15, 17, 15, 7, 23, 7, 7, 17, 0, 17, 7, 15, 7, 7, 39, 15, 31, 7, 15, 7, 7
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OFFSET
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2,2
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COMMENTS
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All nonzero values are >= 7.
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LINKS
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EXAMPLE
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a(3) = 7 because the powers of 2 mod 7 are 2,4,1,2,4,1,2,4,1,2,4,... (and 3 never appears).
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PROG
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(PARI) a216185(n) = {local(k, m); if((omega(n) == 1) && (Mod(n, 2) == Mod(0, 2)), return(0), k=3; while(gcd(k, n) != 1 || (sum(m=0, eulerphi(k) - 1, (Mod(2, k)^m == Mod(n, k))) >= 1), k = k+2)); k} \\ Michael B. Porter, Mar 16 2013
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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