The OEIS mourns the passing of Jim Simons and is grateful to the Simons Foundation for its support of research in many branches of science, including the OEIS.
The OEIS is supported by the many generous donors to the OEIS Foundation.

 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 a(5) > 4*10^9, if it exists. - Giovanni Resta, May 10 2020 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 nonn,more 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 | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified May 19 19:45 EDT 2024. Contains 372703 sequences. (Running on oeis4.)