cp's OEIS Frontend

A337185 Composite numbers k such that A337183(k) is prime.

%I A337185 #19 Feb 06 2021 21:59:50
%S A337185 6,10,15,21,22,26,28,33,35,38,39,42,44,45,46,50,54,62,65,66,68,69,75,
%T A337185 76,77,82,85,95,98,99,102,105,106,111,115,116,117,118,120,123,124,126,
%U A337185 129,132,135,141,143,145,146,152,155,158,161,168,170,176,178,186,188,198,200,201,202,203,205,206
%N A337185 Composite numbers k such that A337183(k) is prime.
%H A337185 Robert Israel, <a href="/A337185/b337185.txt">Table of n, a(n) for n = 1..10000</a>
%e A337185 15 is a term because it is not prime and A337183(15) = 29 is prime.
%p A337185 f:= proc(n) local F, b, i;
%p A337185   F:= sort(map(t -> t[1]$t[2], ifactors(n)[2]), `>`);
%p A337185   b:= convert(F, `+`);
%p A337185   (add(F[i]*b^(i-1), i=1..nops(F)));
%p A337185 end proc:
%p A337185 select(t -> not isprime(t) and isprime(f(t)), [$2..300]);
%Y A337185 Cf. A337183. Disjoint from A001597. Includes 2*k for k in A023209.
%K A337185 nonn,base
%O A337185 1,1
%A A337185 _J. M. Bergot_ and _Robert Israel_, Jan 29 2021