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 A050973 Larger member of friendly pairs ordered by smallest maximal element. 16
 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 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS 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 If we remove duplicates from the sequence we get A095301. - Jeppe Stig Nielsen, Jul 08 2015 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 LINKS Donovan Johnson, Table of n, a(n) for n = 1..10000 Eric Weisstein's World of Mathematics, Friendly Pair. PROG (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 CROSSREFS Cf. A050972, A074902, A095301. Sequence in context: A074233 A201095 A239205 * A095301 A201102 A317680 Adjacent sequences:  A050970 A050971 A050972 * A050974 A050975 A050976 KEYWORD nonn AUTHOR STATUS approved

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Last modified April 15 07:59 EDT 2021. Contains 342975 sequences. (Running on oeis4.)