cp's OEIS Frontend

A144775 Define f(n) = 2 * rad(n) if four divides n and rad(n) otherwise: then a(n) = 0 for composite n where f(n) is not less than n and otherwise equals the number of positive integers k less than n for which f(k) < f(n).

%I A144775 #3 Mar 31 2012 10:28:53
%S A144775 0,1,2,0,4,0,6,3,2,0,10,0,12,0,0,4,16,8,18,0,0,0,22,13,7,0,2,0,28,0,
%T A144775 30,5,0,0,0,16,36,0,0,24,40,0,42,0,21,0,46,16,13,15,0,0,52,11,0,35,0,
%U A144775 0,58,0,60,0,31,5,0,0,66,0,0,0,70,20,72,0,27,0,0,0,78,32,2,0,82,0,0,0,0,55
%N A144775 Define f(n) = 2 * rad(n) if four divides n and rad(n) otherwise: then a(n) = 0 for composite n where f(n) is not less than n and otherwise equals the number of positive integers k less than n for which f(k) < f(n).
%C A144775 This sequence obtains a new maximum a(n) = n - 1 for prime n.
%C A144775 a(n) = 0 often, but not always, when n - 1 and n + 1 are twin primes.
%e A144775 f(8) = 2 * rad(8) = 4. f(k) < 4 for 1, 2 and 3 (f(k) = k for 0 < k < 8); a(8) = 3.
%Y A144775 Cf. A000040, A001097, A007947, A144100, A144774
%K A144775 easy,nonn
%O A144775 1,3
%A A144775 _Reikku Kulon_, Sep 21 2008