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%I #9 Jul 19 2017 21:55:12
%S 1,3,22,70,81,94,115,119,170,214,217,265,310,322,343,364,382,385,400,
%T 472,497,517,527,679,710,742,745,782,820,862,884,889,935,970,1004,
%U 1066,1080,1174,1177,1207,1219,1270,1393,1426,1465,1501,1566,1612,1624,1645
%N Primitive elements of A006532, i.e., which are not product of earlier terms (> 1) in that sequence.
%C If a,b are coprime elements of A006532, their product is again in A006532. But there are some a,b which are not coprime and still a,b,a*b are in A006532: First examples are 820*{2860, 3340, 8580, 10020, 11620, ...}.
%H Donovan Johnson, <a href="/A178492/b178492.txt">Table of n, a(n) for n = 1..10000</a>
%e The terms a(2)=3 and a(3)=22 are coprime elements of A006532, therefore 3*22=66 is a non-primitive element of A006532, and not listed in this sequence.
%o (PARI) for(n=1,1e4, issquare(sigma(n))|next; fordiv( n,d, d>1|next; d*d>n & break; issquare(sigma(d)) & issquare(sigma(n/d)) & next(2) ); print1(n","))
%K nonn
%O 1,2
%A _Farideh Firoozbakht_ and _M. F. Hasler_, Jun 10 2010
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