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Numbers k such that sigma(k) - usigma(k) > 2k.
5

%I #17 Jun 25 2018 03:42:21

%S 1440,1800,2160,2880,3024,3600,4320,5040,5400,5760,6048,6480,7056,

%T 7200,7560,7920,8064,8640,9000,9072,9360,9504,9720,10080,10584,10800,

%U 11088,11520,11880,12096,12240,12600,12960,13680,14040,14112,14400,15120

%N Numbers k such that sigma(k) - usigma(k) > 2k.

%H Giovanni Resta, <a href="/A063846/b063846.txt">Table of n, a(n) for n = 1..10000</a> (first 1000 terms from Harry J. Smith)

%o (PARI) u(n) = sumdiv(n,d, if(gcd(d,n/d)==1,d));

%o j=[]; for(n=1,20000, if(sigma(n)-u(n)>2*n,j=concat(j,n))); j

%o (PARI) u(n) = sumdiv(n, d, if(gcd(d, n/d)==1, d))

%o { n=0; for (m=1, 10^9, if(sigma(m) - u(m) > 2*m, write("b063846.txt", n++, " ", m); if (n==1000, break)) ) } \\ _Harry J. Smith_, Sep 01 2009

%Y Cf. A034448, A048146, A034683, A064597.

%K easy,nonn

%O 1,1

%A _Jason Earls_, Aug 25 2001