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A001837
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Numbers n such that phi(2n+1) < phi(2n).
(Formerly M5406 N2349)
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5
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157, 262, 367, 412, 472, 487, 577, 682, 787, 877, 892, 907, 997, 1072, 1207, 1237, 1312, 1402, 1522, 1567, 1627, 1657, 1732, 1852, 1942, 2047, 2062, 2152, 2194, 2257, 2362, 2437, 2467, 2557, 2572, 2677, 2722, 2782
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history;
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OFFSET
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1,1
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COMMENTS
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Greg Martin (gerg(AT)math.toronto.edu) writes: I recently calculated the smallest solution of phi(30n+1) < phi(30n) (see the Martin link); it has 1116 digits.
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REFERENCES
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J.-M. De Koninck, Ces nombres qui nous fascinent, Entry 157, p. 51, Ellipses, Paris 2008.
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).
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LINKS
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Donovan Johnson, Table of n, a(n) for n = 1..10000
V. L. Klee, Jr., Some remarks on Euler's totient function, Amer. Math. Monthly, 54 (1947), 332.
Greg Martin, The smallest solution of phi(30n+1) < phi(30n) is ..., arXiv:math/9804025 [math.NT], 1998; Amer. Math. Monthly, Vol. 106, No. 5 (1999), pp. 449-451.
J. Shallit, Letter to N. J. A. Sloane, Jul 17 1975
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MAPLE
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with(numtheory, phi); f := proc(n) if phi(2*n+1) < phi(2*n) then RETURN(n) fi end;
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MATHEMATICA
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Select[ Range[4000], EulerPhi[2# + 1] < EulerPhi[2# ] & ]
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PROG
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(PARI) isok(n) = eulerphi(2*n+1) < eulerphi(2*n); \\ Michel Marcus, Oct 03 2017
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CROSSREFS
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Cf. A000010.
Sequence in context: A216498 A275317 A303094 * A142581 A140625 A142874
Adjacent sequences: A001834 A001835 A001836 * A001838 A001839 A001840
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KEYWORD
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nonn
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AUTHOR
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N. J. A. Sloane.
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STATUS
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approved
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