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A236465 Smallest prime a(n) such that 1 + a(1)*a(2)*...*a(n) is prime. 1
2, 2, 3, 3, 2, 13, 2, 11, 19, 2, 2, 5, 11, 2, 31, 53, 3, 31, 43, 19, 13, 11, 43, 23, 7, 5, 13, 5, 29, 2, 29, 17, 53, 157, 13, 13, 3, 5, 127, 7, 97, 5, 97, 2, 89, 61, 7, 71, 61, 5, 127, 113, 37, 191, 107, 17, 197, 37, 101, 2, 5, 7, 17, 457, 3, 19, 29, 103, 227 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Giovanni Resta, Table of n, a(n) for n = 1..500

EXAMPLE

a(1) = 2 because 1 + 2 = 3, which is prime.

a(2) = 2 because 1 + 2 * 2 = 5, which is prime.

a(3) = 3 because 2 doesn't work, since 1 + 2 * 2 * 2 = 9 = 3^2, but 3 does work, giving 1 + 2 * 2 * 3 = 13, which is prime.

MATHEMATICA

pr = 1; Table[p = 2; While[! PrimeQ[p * pr + 1], p = NextPrime@p]; pr *= p; p, {n, 100}] (* Giovanni Resta, Jan 26 2014 *)

CROSSREFS

Cf. A036012, A039726.

Sequence in context: A127684 A036012 A084401 * A131619 A048485 A127714

Adjacent sequences:  A236462 A236463 A236464 * A236466 A236467 A236468

KEYWORD

nonn

AUTHOR

Thomas Ordowski, Jan 26 2014

EXTENSIONS

a(11)-a(69) from Giovanni Resta, Jan 26 2014

STATUS

approved

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Last modified September 17 04:58 EDT 2019. Contains 327119 sequences. (Running on oeis4.)