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A328065
Amicable pairs with the property that the number of divisors of the smaller member is twice the number of divisors of the larger member.
6
220, 284, 12285, 14595, 17296, 18416, 63020, 76084, 69615, 87633, 79750, 88730, 100485, 124155, 122265, 139815, 142310, 168730, 185368, 203432, 308620, 389924, 356408, 399592, 600392, 669688, 609928, 686072, 624184, 691256, 635624, 712216, 643336, 652664, 667964, 783556, 726104, 796696, 898216, 980984
OFFSET
1,1
COMMENTS
Amicable pairs(x,y) such that d(x) = 2*d(y), where d(n) is the number of divisors of n.
LINKS
EXAMPLE
Consider the amicable pair [220, 284]. The smaller member has 12 divisors, they are 1, 2, 4, 5, 10, 11, 20, 22, 44, 55, 110, 220. The larger member has 6 divisors, they are 1, 2, 4, 71, 142, 284. The number of divisors of 220 is twice the number of divisors of 284, so the amicable pair [220, 284] is in the sequence.
MATHEMATICA
seq = {}; s[n_] := DivisorSigma[1, n] - n; Do[m = s[n]; If[m > n && s[m] == n && DivisorSigma[0, n] == 2 * DivisorSigma[0, m], seq = Join[seq, {n, m}]], {n, 1, 10^6}]; seq (* Amiram Eldar, Oct 11 2019 *)
CROSSREFS
Subsequence of A259180 and of A328063.
Sequence in context: A287026 A233538 A328063 * A287011 A333929 A157107
KEYWORD
nonn
AUTHOR
Omar E. Pol, Oct 03 2019
STATUS
approved