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%I #8 Aug 28 2021 06:42:12
%S 1,2,6,6,16,5,3,4,5,33,29,24,31,124,290,103,370,186,4654,133,221,244,
%T 206,726,601,18
%N a(n) is the least k such that Mersenne-prime(n)*prime(k)# + 1 is prime, where prime(k)# is the k-th primorial.
%t 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 *)
%Y Cf. A000043, A000668, A002110, A098570.
%K nonn,more
%O 1,2
%A _Pierre CAMI_, Sep 16 2004
%E a(19)-a(26) from _Amiram Eldar_, Aug 28 2021
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