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%I #13 Jul 14 2012 11:32:31
%S 40859,48505,54385,121771,156125,565607,1154419,1219933,1294363,
%T 2448397,3590461,9710975,16067363,16069573,17984515,19013455,21341755,
%U 25804115,26515223,27656155,29655415,30372605,32101255,34467653,36546355,38043943,38645981,39559219
%N Numbers n such that sigma(n)/phi(n) = 25/16.
%C A subsequence of A011257.
%C If 5^{k+1}-1 = d*D such that p = 2*5^{k+1}*(d+1)-1 and q = 2*(5^{k+1}+D)-1 are distinct primes, then n = 5^k*p*q is a term of this sequence.
%C The same theorem holds for sequences of numbers such that sigma/phi=b^2/(b-1)^2 with other primes b (here b=5), cf. A164646.
%H Donovan Johnson, <a href="/A164648/b164648.txt">Table of n, a(n) for n = 1..1000</a>
%t Select[Range[1000000, 2000000], DivisorSigma[1, #]/EulerPhi[#] == 25/16 &] (* Carl Najafi, Aug 16 2011 *)
%o (PARI) for( n=1,1e7, sigma(n)==25/16*eulerphi(n) && print1(n","))
%Y Cf. A000010 (=phi), A000203 (=sigma), A068390 (sigma/phi=4), A163667 (sigma/phi=9), A164646 (sigma/phi=9/4).
%K nonn
%O 1,1
%A _M. F. Hasler_, Aug 22 2009
%E More terms from _Carl Najafi_, Aug 16 2011
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