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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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3
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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
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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COMMENTS
| Greg Martin (gerg(AT)math.toronto.edu) writes: I recently calculated the smallest solution of phi(30n+1) < phi(30n) (Amer. Math. Monthly 106 (1999), no. 5, 449-451); it has 1116 digits.
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REFERENCES
| J.-M. De Koninck, Ces nombres qui nous fascinent, Entry 157, p. 51, Ellipses, Paris 2008.
V. L. Klee, Jr., Some remarks on Euler's totient function, Amer. Math. Monthly, 54 (1947), 332.
J. O. 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
| Donovan Johnson, Table of n, a(n) for n = 1..10000
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MAPLE
| with(numtheory, phi); f := proc(n) if phi(2*n+1) < phi(2*n) then RETURN(n) fi end;
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MATHEMATICA
| Select[ Range[4000], EulerPhi[2# + 1] < EulerPhi[2# ] & ]
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CROSSREFS
| Cf. A000010.
Sequence in context: A142231 A020356 A142367 * A142581 A140625 A142874
Adjacent sequences: A001834 A001835 A001836 * A001838 A001839 A001840
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KEYWORD
| nonn
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AUTHOR
| N. J. A. Sloane (njas(AT)research.att.com).
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