A156706 - OEIS

%I #8 Nov 24 2019 23:39:26

%S -1,1,-1,1,-1,1,-1,0,-1,1,0,1,-1,1,-1,0,-1,0,-1,1,0,1,-1,1,0,1,-1,0,

%T -1,0,0,1,-1,1,-1,1,-1,0,0,0,0,1,-1,0,-1,1,0,0,-1,1,0,1,0,1,-1,0,-1,0,

%U -1,1,0,0,-1,1,-1,1,0,0,0,1,0,0,0,1,-1,1,-1,0,-1,1,0,0,-1,0,-1,0,-1,0,-1,1,0

%N For all numbers k(n) congruent to +1 or -1 (mod 6) starting with k(n) = {5,7,11,13,...}, a(k(n)) is the congruence (mod 6) if k(n) is prime and 0 if k(n) is composite.

%C Expression for k(n): k(n) = 6*ceiling(n/2) + (-1)^n, so the parity of n gives us the congruence (mod 6) of k(n). - _Daniel Forgues_, Mar 01 2009

%H Daniel Forgues, <a href="/A156706/b156706.txt">Table of n, a(n) for n = 1..33332</a>

%Y Cf. A075743.

%Y The absolute values of this sequence give A075743. The partial sums of this sequence give A156709.

%K sign

%O 1,1

%A _Daniel Forgues_, Feb 13 2009, Feb 14 2009