A233745 - OEIS

A233745

a(n) = smallest number > a(n-1) such that a(1)*a(2)*...*a(n) - 1 is nonprime.

1, 2, 5, 7, 8, 10, 11, 13, 14, 16, 17, 18, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 32, 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, 74, 75, 76

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OFFSET

1,2

COMMENTS

The numbers 3, 4, 6, 8, 9, 12, 15, 19, 30, 31, 81, 152, 390, ... are not in the sequence.

LINKS

Table of n, a(n) for n=1..67.

EXAMPLE

1-1 = 0, 1*2-1 = 1, 1*2*5-1 = 9, 1*2*5*7 - 1 = 69, etc. are nonprimes.

MATHEMATICA

seq={1}; Do[n=Last[seq]+1; While[PrimeQ[n Times@@seq-1], n++]; AppendTo[ seq, n]; , {60}]; seq

CROSSREFS