A227203 Prime(n)^2 mod (prime(n) + prime(n+1)).

4, 1, 1, 13, 1, 19, 1, 25, 9, 1, 9, 43, 1, 49, 9, 9, 1, 9, 73, 1, 9, 85, 9, 109, 103, 1, 109, 1, 115, 49, 133, 9, 1, 25, 1, 9, 9, 169, 9, 9, 1, 25, 1, 199, 1, 241, 253, 229, 1, 235, 9, 1, 25, 9, 9, 9, 1, 9, 283, 1, 25, 49, 313, 1, 319, 49, 9, 25, 1, 355, 9, 379

Offset: 1

Author

Zak Seidov, Sep 18 2013

Keywords

• nonn

Comments

a(n) = 1 if and only if prime(n) and prime(n+1) are twin prime pair (that is, prime(n+1) = 2 + prime(n)).

Crossrefs

Cf. A029707, A167770.

Programs

Mathematica

Table[Mod[Prime[n]^2, Prime[n] + Prime[n + 1]], {n, 200}]
PowerMod[#[[1]],2,Total[#]]&/@Partition[Prime[Range[80]],2,1] (* Harvey P. Dale, Dec 26 2017 *)

PARI

for(n=1,200,print1(prime(n)^2%(prime(n)+prime(n+1))","))