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 A281947 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. 0
 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 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS p - 1 = phi(p) is a totient for all primes p. If A281909(n) is prime, then a(n) = A281909(n). LINKS EXAMPLE 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. PROG (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 CROSSREFS Cf. A000010, A002202, A181062, A281909. Sequence in context: A083809 A092967 A056431 * A199466 A199966 A011027 Adjacent sequences:  A281944 A281945 A281946 * A281948 A281949 A281950 KEYWORD nonn,more AUTHOR Altug Alkan, Feb 03 2017 EXTENSIONS a(19) from Michel Marcus, Feb 04 2017 a(20)-a(28) from Ray Chandler, Feb 08 2017 STATUS approved

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Last modified September 23 00:32 EDT 2021. Contains 347609 sequences. (Running on oeis4.)