A233746 a(1) = 3; for n>3, a(n) = smallest number > a(n-1) such that a(1)*a(2)*...*a(n) + 1 is nonprime.

3, 5, 6, 8, 10, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73

Offset: 1

Author

Michel Lagneau, Dec 15 2013

Keywords

• nonn

Comments

The numbers 1, 2, 4, 7, 9, 11, 32, 322, 498, 685, 880, ... are not in the sequence.

Examples

			3+1 = 4, 3*5+1 = 16, 3*5*6+1 = 91, 3*5*6*8+1 = 721, etc. are nonprimes.
		

Links

• Robert Israel, Table of n, a(n) for n = 1..2000

Crossrefs

Cf. A083769, A233745.

Programs

Maple

A[1]:= 3: P:= 3:
for n from 2 to 100 do
  for k from A[n-1]+1 do
    if not isprime(P*k+1) then
      A[n]:= k; P:= P*k; break
    fi
od od:
seq(A[i],i=1..100); # Robert Israel, Jun 18 2019

Mathematica

seq={3};Do[n=Last[seq]+1;While[PrimeQ[n Times@@seq+1],n++];AppendTo[seq,n];,{100}];seq