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 A333407 Numbers k such that phi(k) = phi(2*k-1) where phi is the Euler totient function (A000010). 1
 1, 1313, 1853, 6683, 12773, 28823, 194123, 198743, 343493, 702923, 829793, 1309853, 1379963, 1846763, 2001203, 2788913, 3911603, 5399363, 5464463, 5689373, 10728113, 11316143, 11776853, 12082073, 14588213, 16587383, 19610063, 20294243, 21470963, 25388963, 28433903 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 LINKS Amiram Eldar, Table of n, a(n) for n = 1..100 EXAMPLE 1313 is a term since 1313 and 2*1313 - 1 = 2625 have the same value of phi: phi(1313) = phi(2625) = 1200. MATHEMATICA seq = {}; Do[If[EulerPhi[n] == EulerPhi[2*n-1], AppendTo[seq, n]], {n, 1, 10^5}]; seq PROG (PARI) isok(k) = eulerphi(k) == eulerphi(2*k-1); \\ Michel Marcus, Mar 20 2020 CROSSREFS Cf. A000010, A092272. Sequence in context: A030646 A223612 A223413 * A221155 A237393 A242151 Adjacent sequences:  A333404 A333405 A333406 * A333408 A333409 A333410 KEYWORD nonn AUTHOR Amiram Eldar, Mar 19 2020 STATUS approved

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Last modified November 29 04:38 EST 2021. Contains 349416 sequences. (Running on oeis4.)