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 A001836 Numbers n such that phi(2n-1) < phi(2n), where phi is Euler's totient function A000010. (Formerly M5429 N2359) 1
 53, 83, 158, 263, 293, 368, 578, 683, 743, 788, 878, 893, 908, 998, 1073, 1103, 1208, 1238, 1268, 1403, 1418, 1502, 1523, 1658, 1733, 1838, 1943, 1964, 2048, 2063, 2153, 2228, 2243, 2258, 2363, 2393, 2423, 2468, 2558, 2573, 2633, 2657, 2678 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 REFERENCES Jeffrey Shallit, personal communication. N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence). N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence). LINKS T. D. Noe, Table of n, a(n) for n = 1..1000 V. L. Klee, Jr., Some remarks on Euler's totient function, Amer. Math. Monthly, 54 (1947), 332. Don Reble, Python program J. Shallit, Letter to N. J. A. Sloane, Jul 17 1975 MAPLE with(numtheory): A001836:=n->`if`(phi(2*n-1) < phi(2*n), n, NULL): seq(A001836(n), n=1..5*10^3); # Wesley Ivan Hurt, Oct 10 2014 MATHEMATICA Select[Range[3000], EulerPhi[2# - 1] < EulerPhi[2#] &] (* Harvey P. Dale, Apr 01 2012 *) PROG (PARI) is(n)=eulerphi(2*n-1)

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Last modified April 21 17:29 EDT 2021. Contains 343156 sequences. (Running on oeis4.)