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A180325 a(n) = k is the smallest number such that n is the number of distinct primes dividing k! + 1. 0
1, 6, 9, 31, 16, 18, 40, 89 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

A greedy inverse to A066856. - R. J. Mathar, Jan 21 2011

LINKS

Table of n, a(n) for n=1..8.

EXAMPLE

a(6) = 18 because the 6 distinct primes dividing 18! + 1 = 6402373705728001

  are {19, 23, 29, 61, 67, 123610951}.

MAPLE

with(numtheory):for n from 1 to 7 do:ind:=0:for k from 1 to 50 while(ind=0)

  do: x:=k!+1:y:=nops(factorset(x)):if y=n then ind:=1:printf(`%d, `, k):else fi:od:

  od:

CROSSREFS

Cf. A038507.

Sequence in context: A086491 A178597 A179908 * A192425 A219687 A147415

Adjacent sequences:  A180322 A180323 A180324 * A180326 A180327 A180328

KEYWORD

nonn,hard

AUTHOR

Michel Lagneau, Jan 18 2011

STATUS

approved

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Last modified April 21 17:36 EDT 2021. Contains 343156 sequences. (Running on oeis4.)