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A152215 Numbers k such that sigma_2(k)/(sigma_1(k)*sigma_0(k)) = c, c an integer. 1

%I #10 Jul 15 2019 03:20:19

%S 1,4,25,100,121,256,289,484,529,841,1156,1600,1681,2116,2209,2809,

%T 3025,3364,3481,5041,6400,6724,6889,7225,7921,8836,10201,11236,11449,

%U 12100,12769,13225,13924,17161,18225,18496,18769,20164,21025,22201,27556,27889,28900

%N Numbers k such that sigma_2(k)/(sigma_1(k)*sigma_0(k)) = c, c an integer.

%C k : A001157(k)/(A000203(k)*A000005(k)) = c, c an integer.

%H Amiram Eldar, <a href="/A152215/b152215.txt">Table of n, a(n) for n = 1..10000</a>

%t Select[Range[50000],IntegerQ[DivisorSigma[2,#]/(DivisorSigma[1,#] DivisorSigma[ 0,#])]&] (* _Harvey P. Dale_, Feb 12 2013 *)

%o (PARI) isok(k) = denominator(sigma(k,2)/(sigma(k, 1)*sigma(k,0))) == 1; \\ _Michel Marcus_, Jul 15 2019

%Y Cf. A000005, A000203, A001157, A003601, A094471, A140480, A003601, A020486, A020487

%K easy,nonn

%O 1,2

%A _Ctibor O. Zizka_, Nov 29 2008

%E More terms from _Harvey P. Dale_, Feb 12 2013

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Last modified March 28 09:04 EDT 2024. Contains 371240 sequences. (Running on oeis4.)