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A050973
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Larger member of friendly pairs ordered by smallest maximal element.
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16
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28, 140, 200, 224, 234, 270, 308, 364, 476, 496, 496, 532, 600, 644, 672, 700, 812, 819, 868, 936, 1036, 1148, 1170, 1204, 1316, 1400, 1484, 1488, 1488, 1540, 1638, 1638, 1638, 1652, 1708, 1800, 1820, 1876, 1988, 2016, 2044, 2200, 2212, 2324
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OFFSET
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1,1
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COMMENTS
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Perfect numbers greater than 6 (A000396) belong to this sequence as they form friendly pairs with smaller perfect, so that the n-th perfect number will appear n-1 times in the sequence. - Michel Marcus, Dec 03 2013
It is possible to derive a friendly pair from 2 existing pairs (a_n,b_n) and (a_k,b_k); if (a_n,b_k) and (a_k,b_n) (resp. (a_k,b_k) and (a_n,b_n)) are coprime, then (a_n*b_k,a_k*b_n) (resp. (a_k*b_k,a_n*b_n)) is a friendly pair. For instance one can derive (32760,30240) from (819,135) and (224,40). Moreover, since 32760/35 and 30240/35 are both coprime to 35, one can also derive the primitive friendly pair (936,864). - Michel Marcus, Oct 09 2015
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LINKS
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PROG
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(PARI) lista(nn) = {for (n=1, nn, ab = sigma(n)/n; for (i=2, n-1, if (sigma(i)/i == ab, print1(n, ", ")); ); ); } \\ Michel Marcus, Dec 03 2013
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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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