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
Amiram Eldar, Table of n, a(n) for n = 1..20000
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
KEYWORD
nonn
AUTHOR
Omar E. Pol, Oct 03 2019
STATUS
approved