

A002093


Highly abundant numbers: numbers n such that sigma(n) > sigma(m) for all m < n.
(Formerly M0553 N0200)


39



1, 2, 3, 4, 6, 8, 10, 12, 16, 18, 20, 24, 30, 36, 42, 48, 60, 72, 84, 90, 96, 108, 120, 144, 168, 180, 210, 216, 240, 288, 300, 336, 360, 420, 480, 504, 540, 600, 630, 660, 720, 840, 960, 1008, 1080, 1200, 1260, 1440, 1560, 1620, 1680, 1800, 1920, 1980, 2100
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OFFSET

1,2


COMMENTS

Where record values of sigma(n) occur.
Also record values of A070172: A070172(i)<a(n) for 1<=i < A085443(n), a(n)=A070172(A085443(n)).  Reinhard Zumkeller, Jun 30 2003
Numbers n such that sum of the even divisors of 2*n is a record. [Arkadiusz Wesolowski, Jul 12 2012]
Conjecture: (a) Every highly abundant number >10 is practical (A005153). (b) For every integer k there exists A such that k divides a(n) for all n>A. Daniel Fischer proved that every highly abundant number greater than 3, 20, 630 is divisible by 2, 6, 12 respectively. The first conjecture has been verified for the first 10000 terms.  Jaycob Coleman, Oct 16 2013


REFERENCES

L. Alaoglu and P. Erdős, On highly composite and similar numbers, Trans. Amer. Math. Soc., 56 (1944), 448469.
Pillai, S. S., Highly abundant numbers, Bull. Calcutta Math. Soc., 35, (1943), 141156
N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).


LINKS

T. D. Noe, Table of n, a(n) for n=1..10000
M. Abramowitz and I. A. Stegun, eds., Handbook of Mathematical Functions, National Bureau of Standards, Applied Math. Series 55, Tenth Printing, 1972 [alternative scanned copy].
D. Fischer, Proof 2, 6, 12 divides a(n) greater than 3, 20, 630 resp.
N. J. A. Sloane, Transforms (The RECORDS transform returns both the highwater marks and the places where they occur).
Wikipedia, Highly abundant number


MATHEMATICA

a={}; k=0; Do[s=DivisorSigma[1, n]; If[s>k, AppendTo[a, n]; k=s], {n, 3000}]; a (* Vladimir Orlovsky, Jul 25 2008 *)


PROG

(PARI) for(n=1, 1000, if(sum(i=1, n1, sign(sigma(n)sigma(i))) == n1, print1(n, ", ")))


CROSSREFS

Cf. A034091, A000203, A004394.
The record values are in A034885.
Cf. A193988, A193989 (records for sigma2 and sigma3).
Sequence in context: A139542 A238616 A093717 * A179971 A067069 A100497
Adjacent sequences: A002090 A002091 A002092 * A002094 A002095 A002096


KEYWORD

nonn,nice


AUTHOR

N. J. A. Sloane.


EXTENSIONS

Better description Apr 15 1997. More terms from Jud McCranie, Jul 04 2000.


STATUS

approved



