cp's OEIS Frontend

A272338 Numbers such that antisigma(n) mod sigma(n) = phi(n), where antisigma(n) is the sum of the numbers less than n that do not divide n, sigma(n) is the sum of the divisors of n and phi(n) is the Euler totient function of n.

%I A272338 #14 May 01 2016 07:45:44
%S A272338 3,9,27,81,243,319,729,2187,3615,6561,8159,9807,19683,32791,59049,
%T A272338 103679,177147,432864,531441,788852,871215,1594323,2779519,2826863,
%U A272338 2858240,4782969,7213536,10036415,14348907,20428863,24423359,29036799,33385279,43046721
%N A272338 Numbers such that antisigma(n) mod sigma(n) = phi(n), where antisigma(n) is the sum of the numbers less than n that do not divide n, sigma(n) is the sum of the divisors of n and phi(n) is the Euler totient function of n.
%C A272338 A000244 is a subset of this sequence.
%H A272338 Giovanni Resta, <a href="/A272338/b272338.txt">Table of n, a(n) for n = 1..73</a> (terms < 2*10^12)
%F A272338 Solutions of the equation  A024816(n) mod A000203(n) = A000010(n).
%e A272338 27*28/2 mod sigma(27) = 378 mod 40 = 18 = phi(27).
%p A272338 with(numtheory): P:=proc(q) local n;
%p A272338 for n from 1 to q do if (n*(n+1)/2) mod sigma(n)=phi(n) then print(n); fi;
%p A272338 od; end: P(10^6);
%t A272338 Select[Range[10^5], Function[n, Mod[Total@ First@ #, Total@ Last@ #] == EulerPhi@ n &@ {Complement[Range@ n, #], #} &@ Divisors@ n]] (* _Michael De Vlieger_, Apr 27 2016 *)
%Y A272338 Cf. A000010, A000203, A000244, A024816, A232324, A272337.
%K A272338 nonn,easy
%O A272338 1,1
%A A272338 _Paolo P. Lava_, Apr 26 2016
%E A272338 a(27)-a(34) from _Giovanni Resta_, May 01 2016