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A291258 a(n) is the smallest number k such that sigma(k) - phi(k) = n*k, or 0 if no such k exists. 0
1, 2, 12, 75960, 17156160 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

COMMENTS

a(5) and following terms > 10^13, if they exist. - Giovanni Resta, Aug 21 2017

LINKS

Table of n, a(n) for n=0..4.

EXAMPLE

a(2) = 12 because sigma(12) = 28, phi(12) = 4; sigma(12) - phi(12) = 2*12 and 12 is the smallest number with this property.

PROG

(PARI) a(n) = {my(k=1); while (sigma(k)-eulerphi(k)!=n*k, k++); k; }

CROSSREFS

Cf. A000010, A000203, A055681.

Sequence in context: A280734 A048830 A038081 * A027737 A063970 A130769

Adjacent sequences:  A291255 A291256 A291257 * A291259 A291260 A291261

KEYWORD

nonn,more

AUTHOR

Altug Alkan, Aug 21 2017

STATUS

approved

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Last modified May 25 01:28 EDT 2019. Contains 323534 sequences. (Running on oeis4.)