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A333973
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Numbers k such that A019320(k) is greater than A064078(k) and the latter is a prime or a prime power.
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1
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OFFSET
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1,1
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COMMENTS
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The unique prime factor of A064078(k) is then a unique prime to base 2 (see A161509), but not a cyclotomic number.
Subsequence of A161508. In fact, subsequence of the set difference A161508 \ A072226.
In all known examples, A064078(k) is a prime. If A064078(k) was a prime power p^j with j>1, then p would be both a Wieferich prime (A001220) and a unique prime to base 2.
Subsequence of A093106 (the characterization of A093106 can be useful when searching for more terms).
Should this sequence be infinite?
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LINKS
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Table of n, a(n) for n=1..9.
Henri Lifchitz and Renaud Lifchitz, Phi(258121,2)/719.
Wikipedia, Unique prime, section Binary unique primes.
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PROG
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(PARI) for(n=1, +oo, c=polcyclo(n, 2); c % n < 2 && next(); c/=(c%n); ispseudoprime(if(ispower(c, , &b), b, c))&&print1(n, ", "))
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CROSSREFS
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Cf. A019320, A064078, A093106, A072226, A144755, A161508, A161509, A247071.
Sequence in context: A265946 A027888 A332925 * A027887 A088383 A067496
Adjacent sequences: A333970 A333971 A333972 * A333974 A333975 A333976
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KEYWORD
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nonn,hard,more
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AUTHOR
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Jeppe Stig Nielsen, Sep 22 2020
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STATUS
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approved
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