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A015840 Numbers n such that phi(n) | sigma(n + 3). 6
1, 2, 3, 4, 7, 8, 12, 14, 19, 20, 21, 24, 27, 30, 32, 39, 52, 63, 84, 91, 102, 112, 117, 127, 129, 132, 135, 155, 165, 181, 200, 210, 252, 327, 348, 387, 403, 405, 410, 432, 452, 453, 456, 459, 475, 480, 532, 549, 592, 620, 624, 679, 693, 714, 725, 952, 1009 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Ivan Neretin, Table of n, a(n) for n = 1..1000

MAPLE

with(numtheory): A015840:=n->`if`(sigma(n+3) mod phi(n) = 0, n, NULL): seq(A015840(n), n=1..5*10^3); # Wesley Ivan Hurt, Feb 04 2017

MATHEMATICA

Select[Range[3000], Divisible[DivisorSigma[1, 3 + #], EulerPhi[#]] &] (* David Nacin, Mar 03 2012 *)

PROG

(PARI) is(n)=!(sigma(n+3)%eulerphi(n)) \\ Charles R Greathouse IV, Sep 25 2012

CROSSREFS

Cf. A020492.

Sequence in context: A122456 A186243 A073882 * A051213 A211659 A301806

Adjacent sequences:  A015837 A015838 A015839 * A015841 A015842 A015843

KEYWORD

nonn

AUTHOR

Robert G. Wilson v

EXTENSIONS

a(1) = 1 added by Ivan Neretin, Jan 30 2017

STATUS

approved

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Last modified April 23 14:15 EDT 2019. Contains 322386 sequences. (Running on oeis4.)