

A066993


Integer of the form phi(n)*sigma(n)/n.


1



1, 4, 13, 20, 24, 36, 40, 65, 64, 84, 112, 96, 128, 121, 171, 186, 200, 216, 168, 208, 192, 273, 312, 340, 392, 364, 480, 448, 456, 496, 612, 605, 576, 640, 768, 768, 840, 880, 840, 936, 960, 1105, 992, 1200, 1093, 1280, 1464, 1364, 1152, 1539, 1152, 1664, 1482
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OFFSET

1,2


LINKS

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


FORMULA

a(n) = sigma(A011775(n))*phi(A011775(n))/A011775(n).


MATHEMATICA

Select[Table[EulerPhi[n] DivisorSigma[1, n]/n, {n, 2000}], IntegerQ] (* Harvey P. Dale, Mar 17 2020 *)


PROG

(PARI) { n=0; for (m=1, 10^10, if ((a=eulerphi(m)*sigma(m)/m) % 1.0 == 0 , write("b066993.txt", n++, " ", a); if (n==1000, return)) ) } \\ Harry J. Smith, Apr 16 2010


CROSSREFS

Cf. A011775.
Sequence in context: A292363 A119048 A241264 * A297884 A298289 A298489
Adjacent sequences: A066990 A066991 A066992 * A066994 A066995 A066996


KEYWORD

nonn


AUTHOR

Benoit Cloitre, Jan 27 2002


EXTENSIONS

Missing term a(43)=992 and new term a(53)=1482 added by Harry J. Smith, Apr 16 2010


STATUS

approved



