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A098571 a(n) is the least k such that Mersenne-prime(n)*prime(k)# + 1 is prime, where prime(k)# is the k-th primorial. 1
1, 2, 6, 6, 16, 5, 3, 4, 5, 33, 29, 24, 31, 124, 290, 103, 370, 186, 4654, 133, 221, 244, 206, 726, 601, 18 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Table of n, a(n) for n=1..26.

MATHEMATICA

f[p_] := Module[{k = 1, q = r = 2}, While[! PrimeQ[r*p + 1], q = NextPrime[q]; r *= q; k++]; k]; f /@ (2^MersennePrimeExponent[Range[15]] - 1) (* Amiram Eldar, Aug 28 2021 *)

CROSSREFS

Cf. A000043, A000668, A002110, A098570.

Sequence in context: A316785 A056136 A349288 * A194120 A161503 A019076

Adjacent sequences:  A098568 A098569 A098570 * A098572 A098573 A098574

KEYWORD

nonn,more

AUTHOR

Pierre CAMI, Sep 16 2004

EXTENSIONS

a(19)-a(26) from Amiram Eldar, Aug 28 2021

STATUS

approved

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Last modified May 26 17:16 EDT 2022. Contains 354092 sequences. (Running on oeis4.)