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A066995 Numbers k such that sigma(k) divides k*phi(k). 1
1, 6, 15, 28, 84, 95, 140, 182, 190, 248, 270, 287, 308, 357, 420, 455, 477, 496, 570, 672, 744, 819, 840, 910, 1199, 1428, 1488, 1547, 1638, 1722, 1848, 1892, 2295, 2398, 2480, 2660, 2730, 3339, 3417, 3472, 3515, 3596, 3640, 3720, 3780, 3956, 4064, 4095 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

A001599 is a subset of this sequence. - Paolo P. Lava, Jan 31 2018

LINKS

Harry J. Smith, Table of n, a(n) for n = 1..1000

MAPLE

with(numtheory): P:=proc(n) if frac(n*phi(n)/sigma(n))=0 then n; fi; end: seq(P(i), i=1..4100); # Paolo P. Lava, Jan 31 2018

MATHEMATICA

Select[Range[4500], Divisible[# EulerPhi[#], DivisorSigma[1, #]]&]  (* Harvey P. Dale, Mar 19 2011 *)

PROG

(PARI) { n=0; for (m=1, 10^10, if ((m*eulerphi(m)) % sigma(m) == 0 , write("b066995.txt", n++, " ", m); if (n==1000, return)) ) } \\ Harry J. Smith, Apr 24 2010

(PARI) isok(n) = frac(n*eulerphi(n)/sigma(n)) == 0; \\ Michel Marcus, Jan 31 2018

(GAP) Filtered([1..10^5], n ->  n*Phi(n) mod Sigma(n) = 0); # Muniru A Asiru, Jan 31 2018

CROSSREFS

Cf. A001599, A011775.

Sequence in context: A115742 A026102 A144519 * A263896 A295979 A180953

Adjacent sequences:  A066992 A066993 A066994 * A066996 A066997 A066998

KEYWORD

nonn

AUTHOR

Benoit Cloitre, Jan 27 2002

STATUS

approved

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Last modified September 27 09:09 EDT 2020. Contains 337380 sequences. (Running on oeis4.)