cp's OEIS Frontend

A227248 Composite numbers such that sum_{i=1..k} (p_i/(p_i+1))/product_{i=1..k} (p_i/(p_i+1)) is an integer, where p_i are the k prime factors of n (with multiplicity).

%I A227248 #9 Jul 04 2013 14:35:01
%S A227248 4,72,102,216,260,264,270,432,462,504,612,720,1980,2592,3672,5184,
%T A227248 5550,8352,10368,15552,20736,22032,25488,29016,30240,31104,36288,
%U A227248 38880,41976,46656,49248,57888,62208,93312,103680,132192,186624,238464,286848,373248,410688
%N A227248 Composite numbers such that sum_{i=1..k} (p_i/(p_i+1))/product_{i=1..k} (p_i/(p_i+1)) is an integer, where p_i are the k prime factors of n (with multiplicity).
%H A227248 Paolo P. Lava, <a href="/A227248/b227248.txt">Table of n, a(n) for n = 1..65</a>
%e A227248 Prime factors of 270 are 2, 3^3, 5; therefore (2/(2+1)+3*3/(3+1)+5/(5+1))/(2/(2+1)*(3/(3+1))^3*5/(5+1)) = 16.
%p A227248 with(numtheory); ListA227248:=proc(q) local a, d, n, p;
%p A227248 for n from 2 to q do if not isprime(n) then p:=ifactors(n)[2];
%p A227248 a:=add((op(1, d)/(op(1, d)+1))*op(2, d), d=p)/mul((op(1, d)/(op(1, d)+1))^op(2, d), d=p);
%p A227248 if type(a, integer) then print(n); fi; fi;
%p A227248 od; end: ListA227248(10^10);
%Y A227248 Cf. A224346, A224912, A226365, A227034.
%K A227248 nonn
%O A227248 1,1
%A A227248 _Paolo P. Lava_, Jul 04 2013