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A015827 Numbers k such that phi(k + 9) | sigma(k). 2
3, 5, 7, 10, 15, 21, 24, 30, 31, 33, 42, 47, 57, 69, 78, 79, 93, 102, 114, 127, 129, 135, 145, 161, 174, 177, 186, 210, 213, 216, 223, 231, 237, 238, 239, 249, 258, 264, 270, 282, 297, 309, 318, 355, 367, 371, 376, 393, 399, 402, 417, 418, 435, 438, 455, 456 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Includes 6*A023204.  Thus Dickson's conjecture implies the sequence is infinite. - Robert Israel, Jan 10 2019

LINKS

Vincenzo Librandi, Table of n, a(n) for n = 1..3000

MAPLE

filter:= n -> (numtheory:-sigma(n)/numtheory:-phi(n+9))::integer:

select(filter, [$1..1000]); # Robert Israel, Jan 10 2019

MATHEMATICA

Select[Range[1000], Divisible[DivisorSigma[1, #], EulerPhi[9 + #]] &] (* David Nacin, Mar 01 2012 *)

PROG

(PARI) is(n)=sigma(n)%(eulerphi(n)+9)==0 \\ Charles R Greathouse IV, Sep 25 2012

CROSSREFS

Cf. A015849, A023204.

Sequence in context: A140261 A310021 A310022 * A310023 A310024 A088635

Adjacent sequences:  A015824 A015825 A015826 * A015828 A015829 A015830

KEYWORD

nonn,changed

AUTHOR

Robert G. Wilson v

STATUS

approved

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Last modified January 21 11:44 EST 2019. Contains 319354 sequences. (Running on oeis4.)