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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.
2
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
1,1
COMMENTS
The numbers 1, 2, 4, 7, 9, 11, 32, 322, 498, 685, 880, ... are not in the sequence.
LINKS
EXAMPLE
3+1 = 4, 3*5+1 = 16, 3*5*6+1 = 91, 3*5*6*8+1 = 721, etc. are nonprimes.
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
CROSSREFS
Sequence in context: A193599 A068125 A139437 * A299233 A320997 A083042
KEYWORD
nonn
AUTHOR
Michel Lagneau, Dec 15 2013
STATUS
approved