A015827 Numbers k such that phi(k + 9) | sigma(k).
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
Offset: 1
Keywords
Links
- Vincenzo Librandi, Table of n, a(n) for n = 1..3000
Programs
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Maple
filter:= n -> (numtheory:-sigma(n)/numtheory:-phi(n+9))::integer: select(filter, [$1..1000]); # Robert Israel, Jan 10 2019
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Mathematica
Select[Range[1000], Divisible[DivisorSigma[1, #], EulerPhi[9 + #]] &] (* David Nacin, Mar 01 2012 *)
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PARI
is(n)=sigma(n)%(eulerphi(n)+9)==0 \\ Charles R Greathouse IV, Sep 25 2012
Comments