A208767 - OEIS

A208767

Generalized 2-super abundant numbers.

1, 2, 4, 6, 12, 24, 48, 60, 120, 240, 360, 720, 840, 1680, 2520, 5040, 10080, 15120, 25200, 27720, 55440, 110880, 166320, 277200, 332640, 360360, 720720, 1441440, 2162160, 3603600, 4324320, 7207200, 10810800, 12252240, 21621600, 24504480, 36756720, 61261200

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OFFSET

1,2

COMMENTS

The generalized k-super abundant numbers are those such that sigma_k(n)/(n^k) > sigma_k(m)/(m^k) for all m < n, where sigma_k(n) is the sum of the k-th powers of the divisors of n.

1-super abundant numbers are A004394. 0-super abundant numbers are A002182.

Pillai called these numbers "highly abundant numbers of the 2nd order". - Amiram Eldar, Jun 30 2019

LINKS

Amiram Eldar, Table of n, a(n) for n = 1..251

S. Sivasankaranarayana Pillai, Highly abundant numbers, Bulletin of the Calcutta Mathematical Society, Vol. 35, No. 1 (1943), pp. 141-156.

S. Sivasankaranarayana Pillai, On numbers analogous to highly composite numbers of Ramanujan, Rajah Sir Annamalai Chettiar Commemoration Volume, ed. Dr. B. V. Narayanaswamy Naidu, Annamalai University, 1941, pp. 697-704.

Srinivasa Ramanujan, Highly composite numbers, Annotated and with a foreword by Jean-Louis Nicolas and Guy Robin, The Ramanujan Journal, Vol. 1, No. 2 (1997), pp. 119-153, alternative link.

FORMULA

Limit_{n->oo} A001157(a(n))/a(n)^2 = zeta(2) (A013661). - Amiram Eldar, Sep 25 2022

EXAMPLE

For i=24, sigma_2(24)/(24^2)=850/576=1.47569, a new record, thus 24 is in the sequence.

MATHEMATICA

s = {1}; a = 1; Do[ If[DivisorSigma[2, n]/(n^2) > a, a = DivisorSigma[2, n]/(n^2); AppendTo[s, n]], {n, 10000000}]; s

CROSSREFS

Cf. A002182, A004394, A004490, A002201, A001157, A013661, A017667, A017668.

Subsequence of A025487.

Sequence in context: A068010 A375438 A095848 * A136339 A019505 A350049

Adjacent sequences: A208764 A208765 A208766 * A208768 A208769 A208770

KEYWORD