login
The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A094783 Numbers n such that, for all m < n, d_i(n) <= d_i(m) for i=1 to Min(d(n),d(m)), where d_i(n) denotes the i-th smallest divisor of n. 6
1, 2, 4, 6, 12, 24, 48, 60, 120, 240, 360, 1680, 2520, 5040, 10080, 15120, 25200, 27720, 55440, 110880, 166320, 277200, 720720, 1441440, 2162160, 3603600, 7207200, 10810800, 122522400, 183783600, 2327925600, 3491888400, 80313433200 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

The function d(n) (A000005) is the number of divisors of n.

The defining criterion for this sequence is a sufficient, but not necessary, condition for membership in A095849.

Subsequence of A002182. - David Wasserman, Jun 28 2007

Why is 720 not in the sequence? The divisors of 360 begin 1,2,3,4,5,6,8,9,10,12,15,18 and the divisors of 720 begin 1,2,3,4,5,6,8,9,10,12,15,16. - J. Lowell, Aug 23 2007 [Answer from Don Reble, Sep 11 2007: 720 is precluded by 420. (1,2,3,4,5,6,7,10,12,14,15,20,21,...)]

Conjecture: If n is in this sequence, then so is the smallest number with n divisors. (This conjecture is definitely false for A002182 (n=840) and A019505 (n=240.) - J. Lowell, Jan 24 2008

LINKS

Table of n, a(n) for n=1..33.

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].

M. Abramowitz and I. A. Stegun, eds., Handbook of Mathematical Functions, National Bureau Of Standards Applied Math. Series 55, Tenth Printing, 1972, p. 844.

J. Britton, Perfect Number Analyzer.

Wikipedia, Table of divisors.

EXAMPLE

As n increases, the positive integer n=6 sets or ties the existing records for smallest first, second and third-smallest divisors (1, 2 and 3), as well as for its fourth-smallest (6). Since no smaller integer has more than three divisors, 6 satisfies the requirement for this sequence.

CROSSREFS

Cf. A123258.

Sequence in context: A135614 A115387 A095849 * A058764 A087009 A168263

Adjacent sequences:  A094780 A094781 A094782 * A094784 A094785 A094786

KEYWORD

nonn

AUTHOR

Matthew Vandermast, Jun 10 2004

EXTENSIONS

More terms from David Wasserman, Jun 28 2007

Definition corrected by Ray Chandler, May 05 2008

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified February 17 17:59 EST 2020. Contains 331999 sequences. (Running on oeis4.)