A114064 - OEIS

A114064

Numbers k such that tau(k) does not divide sigma(k)*phi(k), where tau(k) = A000005(k).

2, 4, 12, 16, 25, 36, 48, 64, 75, 80, 81, 100, 112, 121, 144, 162, 192, 208, 225, 240, 256, 272, 289, 300, 320, 324, 336, 363, 368, 400, 405, 448, 484, 512, 529, 560, 567, 576, 592, 624, 688, 700, 704, 720, 729, 752, 768, 784, 810, 816, 841, 848, 867, 900

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,1

LINKS

Table of n, a(n) for n=1..54.

EXAMPLE

tau(400) = 15 = 3*5 does not divide phi(400)*sigma(400) = 153760 = 2^5 * 5 * 31^2.

PROG

(PARI) isok(n) = sigma(n)*eulerphi(n) % numdiv(n); \\ Michel Marcus, Jan 08 2014

CROSSREFS

Sequence in context: A171943 A225748 A358231 * A071118 A132314 A053636

Adjacent sequences: A114061 A114062 A114063 * A114065 A114066 A114067

KEYWORD

nonn

AUTHOR

Giovanni Resta, Feb 13 2006

STATUS

approved