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A281947
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Smallest prime p such that p^i - 1 is a totient (A002202) for all i = 1 to n, or 0 if no such p exists.
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0
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2, 3, 7, 7, 37, 37, 113, 113, 241, 241, 241, 241, 241, 241, 241, 241, 241, 241, 2113, 2113, 2113, 2113, 2113, 2113, 3121, 3121, 3121, 3121
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OFFSET
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1,1
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COMMENTS
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p - 1 = phi(p) is a totient for all primes p.
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LINKS
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EXAMPLE
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a(3) = 7 because 7^2 - 1 = 48, 7^3 - 1 = 342 are both totient numbers (A002202) and 7 is the least prime number with this property.
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PROG
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(PARI) isok(p, n)=for (i=1, n, if (! istotient(p^i-1), return(0)); ); 1;
a(n) = {my(p=2); while (! isok(p, n), p = nextprime(p+1)); p; } \\ Michel Marcus, Feb 04 2017
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CROSSREFS
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KEYWORD
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nonn,more
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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