login
This site is supported by donations to The OEIS Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A057600 a(n) is smallest number m such that (m = product of n distinct primes) and all divisors of m are lucky numbers. 1
3, 21, 777, 61383 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

a(5)>2*10^7, if it exists. - Vit Planocka (planocka(AT)mistral.cz), Sep 26 2003

LINKS

Table of n, a(n) for n=1..4.

EXAMPLE

a(2) = 3*7 = 21: divisors of 21 are 1, 3, 7, 21, all of which are lucky numbers.

MATHEMATICA

lst = Range[1, 2*10^7, 2]; i = 2; While[ i <= (len = Length@lst) && (k = lst[[i]]) <= len, lst = Drop[lst, {k, len, k}]; i++ ]; fQ[n_] := Block[{d = Rest@Divisors@n, k = 1, lmt = DivisorSigma[0, n]}, While[k < lmt && MemberQ[lst, d[[k]]], k++ ]; k == lmt]; t = Table[0, {10}]; Do[ If[ fQ@lst[[n]], a = Length@ FactorInteger@lst[[n]]; If[ t[[a]] == 0, t[[a]] = lst[[n]]; Print[ lst[[n]] ]]], {n, 2, Length@lst}] (* Robert G. Wilson v, May 12 2006 *)

CROSSREFS

Cf. A000959.

Sequence in context: A001699 A291967 A171104 * A162924 A079269 A127104

Adjacent sequences:  A057597 A057598 A057599 * A057601 A057602 A057603

KEYWORD

more,nonn

AUTHOR

Naohiro Nomoto, Oct 06 2000

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 | More pages
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified October 19 22:00 EDT 2018. Contains 316378 sequences. (Running on oeis4.)