A180325 a(n) = k is the smallest number such that n is the number of distinct primes dividing k! + 1.

1, 6, 9, 31, 16, 18, 40, 89

Offset: 1

Author

Michel Lagneau, Jan 18 2011

Keywords

• nonn
• hard

Comments

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

Examples

			a(6) = 18 because the 6 distinct primes dividing 18! + 1 = 6402373705728001
  are {19, 23, 29, 61, 67, 123610951}.
		

Crossrefs

Cf. A038507.

Programs

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: