cp's OEIS Frontend

A285615 Numbers k such that usigma(k) >= 3*k, where usigma(k) = sum of unitary divisors of k (A034448).

%I A285615 #25 Aug 16 2021 22:34:56
%S A285615 30030,39270,43890,46410,51870,53130,62790,66990,67830,71610,79170,
%T A285615 82110,84630,85470,91770,94710,99330,101010,103530,108570,111930,
%U A285615 117390,122430,128310,136290,140910,144690,154770,161070,164010,166530,168630,182490,191730
%N A285615 Numbers k such that usigma(k) >= 3*k, where usigma(k) = sum of unitary divisors of k (A034448).
%C A285615 Unitary 3-abundant numbers, correspond to 3-abundant numbers (A023197).
%C A285615 Similarly, the first numbers k such that usigma(k) >= 4*k are 200560490130, 7420738134810, 8222980095330, and 8624101075590. - _Giovanni Resta_, Apr 23 2017
%C A285615 The least odd term in this sequence is A070826(17) = 961380175077106319535 and the least odd number k such that usigma(k) >= 4*k is A070826(52) = 5.312...*10^95. - _Amiram Eldar_, Dec 26 2020
%H A285615 Amiram Eldar, <a href="/A285615/b285615.txt">Table of n, a(n) for n = 1..100</a>
%t A285615 usigma[n_] := If[n == 1, 1, Times @@ (1 + Power @@@ FactorInteger[n])]; Select[Range[100000], usigma[#] >= 3*# &]
%o A285615 (PARI) isok(k) = sumdivmult(k, d, if(gcd(d, k/d)==1, d)) >= 3*k; \\ _Michel Marcus_, Dec 26 2020
%Y A285615 Cf. A034448, A023197, A034683, A070826.
%K A285615 nonn
%O A285615 1,1
%A A285615 _Amiram Eldar_, Apr 22 2017