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A178492
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Primitive elements of A006532, i.e., which are not product of earlier terms (> 1) in that sequence.
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1
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1, 3, 22, 70, 81, 94, 115, 119, 170, 214, 217, 265, 310, 322, 343, 364, 382, 385, 400, 472, 497, 517, 527, 679, 710, 742, 745, 782, 820, 862, 884, 889, 935, 970, 1004, 1066, 1080, 1174, 1177, 1207, 1219, 1270, 1393, 1426, 1465, 1501, 1566, 1612, 1624, 1645
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OFFSET
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1,2
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COMMENTS
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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, ...}.
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LINKS
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EXAMPLE
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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.
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PROG
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(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", "))
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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