The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A074838 Numbers m such that sum(d|m, 1/core(d) ) is an integer where core(x) is the squarefree part of x. 1

%I

%S 1,6,8,16,20,24,54,60,72,96,126,128,180,216,243,256,384,441,486,500,

%T 504,540,648,704,729,864,891,972,1100,1152,1260,1500,1536,1620,1782,

%U 1792,1944,2016,2048,2112,2205,2560,3300,3456,3528,3564,3645,3888,4096

%N Numbers m such that sum(d|m, 1/core(d) ) is an integer where core(x) is the squarefree part of x.

%H Amiram Eldar, <a href="/A074838/b074838.txt">Table of n, a(n) for n = 1..1000</a>

%t f[p_, e_] := If[OddQ[e], p, 1]; sqf[n_] := Times @@ (f @@@ FactorInteger[n]); seqQ[n_] := IntegerQ @ DivisorSum[n, 1/sqf[#] &]; Select[Range[2^12], seqQ] (* _Amiram Eldar_, Apr 02 2020 *)

%o (PARI) isok(m) = denominator(sumdiv(m, d, 1/core(d))) == 1; \\ _Michel Marcus_, Apr 02 2020

%Y Cf. A007913.

%K nonn

%O 1,2

%A _Benoit Cloitre_, Sep 09 2002

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified August 4 21:32 EDT 2021. Contains 346455 sequences. (Running on oeis4.)