This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A204828 #19 Feb 16 2025 08:33:16 %S A204828 120,180,240,360,420,480,504,540,600,660,672,720,780,840,900,960,1008, %T A204828 1080,1200,1260,1320,1344,1440,1512,1560,1584,1620,1680,1800,1848, %U A204828 1872,1890,1920,1980,2016,2040,2100,2160,2184,2280,2340,2352,2376,2400,2520,2640 %N A204828 Numbers n with abundancy 3 <= sigma(n)/n < 4. %C A204828 A subsequence of A023197 (numbers n such that sigma(n) >= 3n) which is in turn a subsequence of the abundant numbers A005101, i.e., numbers n with sigma(n)/n > 2. %C A204828 Differs from A023197 from a(565) on: The first term of A023197 which is not in this sequence is A023197(565) = 27720 = A023198(1) = A023199(4), the least number with abundancy >= 4. %C A204828 Numbers with abundancy sigma(n)/n < 2 are called deficient and listed in A005100. Numbers with sigma(n)/n in the interval [2,3) are listed in A204829. Numbers with sigma(n)/n in the interval [4,5) are listed in A230608. - _M. F. Hasler_, Dec 05 2013 %H A204828 Jaroslav Krizek, <a href="/A204828/b204828.txt">Table of n, a(n) for n = 1..3000</a> %H A204828 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/Abundancy.html">Abundancy</a> %H A204828 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/AbundantNumber.html">Abundant Number</a> %e A204828 Number 180 is in the sequence because sigma(180)/180 = 546/180 = 3.0333... %Y A204828 Cf. A204829 (abundant numbers with abundancy 2 <= a < 3). %K A204828 nonn %O A204828 1,1 %A A204828 _Jaroslav Krizek_, Jan 22 2012