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%I #20 Sep 09 2017 19:27:12
%S 0,1,1,1,1,1,1,1,1,0,1,1,1,0,1,1,1,1,1,0,1,0,1,1,1,0,1,0,1,0,1,1,0,0,
%T 1,1,1,0,0,0,1,0,1,0,1,0,1,1,1,0,0,0,1,1,1,0,0,0,1,0,1,0,1,1,1,0,1,0,
%U 0,0,1,1,1,0,1,0,1,0,1,0,1,0,1,0,1,0,0,0,1,0,1,0,0,0,1,1,1,0,0,0,1,0,1,0,1,0,1,1,1,0,0,0,1,0,1,0,0,0,1,0
%N Characteristic function for A251726: a(n) = 1 if n > 1 and gpf(n) < spf(n)^2, otherwise 0; here spf(n) and gpf(n) (smallest and greatest prime factor of n) are sequences A020639(n) and A006530(n).
%C a(n) = 1 if n > 1 and there exists r <= A006530(n) such that r^k <= A020639(n) and A006530(n) < r^(k+1) for some k >= 0, otherwise 0 (the original definition).
%H Antti Karttunen, <a href="/A252372/b252372.txt">Table of n, a(n) for n = 1..10000</a>
%F Other identities. For all n >= 1:
%F a(n) = a(A066048(n)). [The result depends only on the smallest and the largest prime factor of n.]
%o (Scheme) (define (A252372 n) (if (< (A252375 n) (+ 1 (A006530 n))) 1 0))
%Y Characteristic function of A251726.
%Y A252373 gives the partial sums.
%Y Cf. A006530, A020639, A066048, A252459, A252757.
%K nonn
%O 1
%A _Antti Karttunen_, Dec 17 2014. A new simpler definition found Jan 04 2015 and the original definition moved to the Comments section.