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Odd composites k such that A342926(2*k) is a multiple of 3.
1

%I #6 Feb 23 2022 21:50:14

%S 15,33,45,51,69,87,99,105,123,135,141,147,153,159,165,175,177,195,207,

%T 213,231,249,255,261,267,285,297,303,315,321,325,339,345,357,369,375,

%U 393,405,411,423,429,435,441,447,459,465,475,477,483,495,501,507,519,531,537,555,561,573,585,591,609,615,621,627,639

%N Odd composites k such that A342926(2*k) is a multiple of 3.

%H <a href="/index/Si#SIGMAN">Index entries for sequences related to sigma(n)</a>

%o (PARI)

%o A003415(n) = if(n<=1, 0, my(f=factor(n)); n*sum(i=1, #f~, f[i, 2]/f[i, 1]));

%o A342926(n) = (A003415(sigma(n))-n);

%o isA351562(n) = ((n%2)&&!isprime(n)&&!(A342926(2*n)%3));

%Y Cf. A000203, A003415, A342925, A342926, A347880.

%Y Cf. A347874 (the intersection of this sequence and A347872).

%K nonn

%O 1,1

%A _Antti Karttunen_, Feb 23 2022