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%I #12 Dec 30 2019 13:26:19
%S 2,2,2,6,30,10,4,26,12,10,12,436,644,424,2164,862,408,9558,5226,12350
%N Least k such that k*M#(n) + 1 is prime where M#(n) is the product of the first n Mersenne primes = Product_{j=1..n} A000668(j).
%e 2*(2^2-1)*(2^3-1)*(2^5-1) + 1 = 1303 prime so a(3)=2.
%t With[{s = FoldList[Times, Array[2^MersennePrimeExponent@ # - 1 &, 16]]}, Array[Block[{k = 2}, While[! PrimeQ[k s[[#]] + 1], k++]; k] &, Length@ s]] (* _Michael De Vlieger_, Dec 27 2019 *)
%K hard,more,nonn
%O 1,1
%A _Pierre CAMI_, Oct 17 2004
%E a(15)-a(20) from _Donovan Johnson_, Mar 23 2008
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