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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
OFFSET
1,2
COMMENTS
A greedy inverse to A066856. - R. J. Mathar, Jan 21 2011
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
KEYWORD
nonn,hard
AUTHOR
Michel Lagneau, Jan 18 2011
STATUS
approved