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 A270539 Primes p such that gcd(phi(p-1), sigma(p-1)) = 1 with phi = A000010, sigma = A000203. 1
 2, 3, 5, 17, 37, 101, 257, 401, 577, 1297, 1601, 2917, 4357, 8101, 8837, 12101, 13457, 14401, 22501, 25601, 28901, 30977, 32401, 33857, 41617, 52901, 55697, 57601, 62501, 65537, 69697, 72901, 80657, 90001, 93637, 115601, 147457, 160001, 193601, 217157, 220901 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Fermat primes (A019434) are terms. LINKS Jaroslav Krizek, Table of n, a(n) for n = 1..200 EXAMPLE Prime 17 is a term because gcd(sigma(16), phi(16)) = gcd(31, 8) = 1. PROG (Magma) [n: n in [1..10^6] | IsPrime(n) and GCD(SumOfDivisors(n-1), EulerPhi(n-1)) eq 1] (PARI) isok(p) = isprime(p) && (gcd(eulerphi(p-1), sigma(p-1)) == 1); \\ Michel Marcus, Oct 06 2021 CROSSREFS Cf. A000010, A000203, A019434. Sequence in context: A259596 A189536 A163588 * A053182 A348153 A211972 Adjacent sequences: A270536 A270537 A270538 * A270540 A270541 A270542 KEYWORD nonn AUTHOR Jaroslav Krizek, Jul 12 2016 STATUS approved

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Last modified February 28 04:16 EST 2024. Contains 370379 sequences. (Running on oeis4.)