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Number of values of k, 0 < k < n, for which (2*n^2 + 2*k*n - k^2 - k)/2 is prime.
0

%I #25 Jul 16 2018 04:53:00

%S 0,0,1,1,1,1,1,1,2,2,2,2,0,3,3,1,3,5,2,2,4,2,1,4,3,2,4,1,4,4,2,4,4,3,

%T 1,3,2,4,12,3,2,7,1,7,15,3,4,6,3,8,8,2,4,10,6,7,7,3,6,16,3,4,6,3,8,7,

%U 4,5,11,5,4,7,5,8,12,2,12,8,4,16,9,3,8,24,6,8,11,5,8,19,3

%N Number of values of k, 0 < k < n, for which (2*n^2 + 2*k*n - k^2 - k)/2 is prime.

%C It appears that a(A046174(n)) = 0.

%o (PARI) a(n) = sum(k=1, n-1, isprime((2*n^2+2*k*n-k^2-k)/2))

%Y Cf. A046174.

%K nonn

%O 0,9

%A _Gionata Neri_, Jul 08 2018