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a(n) = 1 if the n-th prime == 1 mod 6, otherwise a(n) = 0.
4

%I #5 Jun 26 2019 11:05:07

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

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

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

%N a(n) = 1 if the n-th prime == 1 mod 6, otherwise a(n) = 0.

%H <a href="/index/Ch#char_fns">Index entries for characteristic functions</a>

%t Table[Mod[Mod[Mod[Mod[Prime[k], 6], 5], 3], 2], {k, 1, 120}]

%o (PARI) a(n) = (prime(n) % 6) == 1; \\ _Michel Marcus_, Jun 26 2019

%Y Cf. A000040, A039704, A091178.

%K nonn

%O 1,1

%A Joseph Biberstine (jrbibers(AT)indiana.edu), Nov 19 2004