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A202448 Least k such that k*n!! +1 is a prime number. 0

%I

%S 1,1,2,2,2,2,2,2,8,2,10,3,2,6,10,3,2,2,14,5,10,9,6,2,22,10,4,2,26,2,

%T 22,3,8,11,30,11,6,4,2,15,52,10,22,13,10,9,34,11,18,18,2,10,26,12,4,

%U 34,4,18,26,16,34,25,22,12,14,32,50,24,4,8,12,14,26,4

%N Least k such that k*n!! +1 is a prime number.

%e a(9) = 8 because 8*9!! + 1 = 8*945 + 1 = 7561 is prime.

%t Table[k = 0; While[!PrimeQ[k*n!! +1], k++]; k, {n, 85}]

%Y Cf. A006882.

%K nonn

%O 1,3

%A _Michel Lagneau_, Dec 19 2011

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Last modified January 17 04:08 EST 2022. Contains 350377 sequences. (Running on oeis4.)