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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
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
KEYWORD
nonn,more
AUTHOR
Naohiro Nomoto, Oct 06 2000
STATUS
approved

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