cp's OEIS Frontend

A325966 a(n) is the largest i <= sigma(n)-A020639(n) such that n-i and n-(sigma(n)-i) are relatively prime.

%I A325966 #8 Jun 02 2019 00:52:08
%S A325966 0,1,0,5,0,7,0,13,10,15,0,25,0,21,20,29,0,37,0,39,28,33,0,55,26,39,36,
%T A325966 29,0,67,0,61,44,51,42,89,0,57,52,87,0,91,0,81,74,69,0,121,50,91,68,
%U A325966 95,0,115,66,117,76,87,0,163,0,93,100,125,78,139,0,121,92,141,0,193,0,111,120,137,88,163,0,183,118,123,0
%N A325966 a(n) is the largest i <= sigma(n)-A020639(n) such that n-i and n-(sigma(n)-i) are relatively prime.
%H A325966 Antti Karttunen, <a href="/A325966/b325966.txt">Table of n, a(n) for n = 1..16384</a>
%H A325966 Antti Karttunen, <a href="/A325966/a325966.txt">Data supplement: n, a(n) computed for n = 1..65537</a>
%H A325966 <a href="/index/Si#SIGMAN">Index entries for sequences related to sigma(n)</a>
%F A325966 a(n) = A000203(n) - A325965(n).
%F A325966 For all n:
%F A325966 a(A000396(n)) = A000396(n)+1.
%F A325966 a(n) <= A325818(n).
%o A325966 (PARI)
%o A325966 A020639(n) = if(1==n, n, factor(n)[1, 1]);
%o A325966 A325966(n) = { my(s=sigma(n)); forstep(i=s-A020639(n), 0, -1, if(1==gcd(n-i, n-(s-i)), return(i))); };
%Y A325966 Cf. A000203, A000396, A020639, A324213, A325818, A325961, A325962, A325965.
%K A325966 nonn
%O A325966 1,4
%A A325966 _Antti Karttunen_, May 29 2019