A280314 Relationship of prime numbers to multiples of 6. The value of a(n) = 2 if n*6 has two neighboring primes, a(n) = 1 if only n*6+1 is prime, a(n) = -1 if only n*6-1 is prime, and a(n) = 0 if the neighbors of n*6 are both composite.
2, 2, 2, -1, 2, 1, 2, -1, -1, 2, 1, 2, 1, -1, -1, 1, 2, 2, -1, 0, 1, -1, 2, 0, 2, 1, 1, -1, -1, 2, 0, 2, 2, 0, 1, 0, 1, 2, -1, 2, 0, -1, -1, -1, 2, 1, 2, 0, -1, 0, 1, 2, -1, 0, 1, 1, 0, 2, -1, -1, 1, 1, 1, -1, -1, 1, -1, 1, 0, 2, 0, 2, 1, -1, -1, 1, 2, -1, 0, -1, 1, -1, 1, -1, -1, 0, 2, 0, 0, 1, 1
Offset: 1
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Examples
From _Michael De Vlieger_, Dec 31 2016: (Start) a(1) = 2 since both 1(6)-1 = 5 and 1(6)+1 = 7 are prime. a(4) = -1 since only 4(6)-1 = 23 is prime; 4(6)+1 = 25 is divisible by 5. a(20) = 0 since neither 20(6)-1 = 119 nor 20(6)+1 = 121 are prime. (End)
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Mathematica
Table[If[Times @@ Abs@ # == 1, Total@ Abs@ #, Total@ #] &[{-1, 1} Boole@ Map[PrimeQ, n + {-1, 1}]], {n, 6, 546, 6}] (* Michael De Vlieger, Dec 31 2016 *)
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