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Least nonnegative k such that n!-k is semiprime.
1

%I #8 Aug 28 2022 23:15:36

%S 0,2,1,2,7,1,2,1,5,3,1,19,11,1,19,19,11,1,19,23,1,1,47,1,1,29,3,29,2,

%T 59,73,1,43,1,13,17,41,1,2,5,3,53,79,7,1,53,23,1,13,13,61,7,59,61,7,

%U 31,1,89,107,103,67,47,103,19,43,1,71,11,7,83,79,67,71

%N Least nonnegative k such that n!-k is semiprime.

%C Semiprime analog of A033933. After n = 3, a(n) is never again 0.

%F a(n) = Min_{k such that n!-k is in A001358 and k>=0}.

%e a(3) = 0 because 3! - 0 = 6 - 0 = 6 = 2 * 3.

%e a(4) = 2 because 4! - 2 = 24 - 2 = 22 = 2 * 11.

%e a(5) = 1 because 5! - 1 = 119 = 7 * 17.

%Y Cf. A001358, A033933, A356207.

%K nonn

%O 3,2

%A _Jonathan Vos Post_, Sep 24 2007

%E More terms from _Jinyuan Wang_, Aug 28 2022