A204828 Numbers n with abundancy 3 <= sigma(n)/n < 4.

120, 180, 240, 360, 420, 480, 504, 540, 600, 660, 672, 720, 780, 840, 900, 960, 1008, 1080, 1200, 1260, 1320, 1344, 1440, 1512, 1560, 1584, 1620, 1680, 1800, 1848, 1872, 1890, 1920, 1980, 2016, 2040, 2100, 2160, 2184, 2280, 2340, 2352, 2376, 2400, 2520, 2640

Offset: 1

Author

Jaroslav Krizek, Jan 22 2012

Keywords

• nonn

Comments

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.

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.

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

Examples

			Number 180 is in the sequence because sigma(180)/180 = 546/180 = 3.0333...
		

Links

• Jaroslav Krizek, Table of n, a(n) for n = 1..3000
• Eric Weisstein's World of Mathematics, Abundancy
• Eric Weisstein's World of Mathematics, Abundant Number

Crossrefs

Cf. A204829 (abundant numbers with abundancy 2 <= a < 3).