A140366 a(n) = isprime(6n-1) + 2*isprime(6n-5), where isprime = A010051.

1, 3, 3, 3, 1, 2, 3, 3, 1, 1, 2, 3, 2, 3, 1, 0, 3, 3, 3, 0, 0, 3, 1, 2, 1, 2, 2, 3, 1, 1, 2, 1, 3, 2, 0, 2, 0, 3, 3, 1, 2, 1, 1, 1, 1, 2, 3, 2, 1, 0, 0, 3, 3, 0, 0, 2, 2, 1, 3, 1, 0, 2, 2, 3, 1, 0, 3, 0, 2, 1, 2, 1, 2, 3, 1, 0, 3, 3, 0, 1, 0, 3, 0, 3, 1, 0, 1

Offset

1,2

Comments

The idea is to consider 2-bit words, where the least resp. most significant bit correspond to primality of the respective member in the couple (6n-1,6n-5). (It might have been more natural to inverse the correspondences, i.e. to associate the LSB to the smaller number of the pair.) - M. F. Hasler, Jun 16 2008

Links

Table of n, a(n) for n=1..87.

Mathematica

a[n_]:=Boole[PrimeQ[6n-1]]+2Boole[PrimeQ[6n-5]]; Array[a, 87] (* James C. McMahon, Jul 08 2025 *)

Prog

(PARI) a(n)=isprime(6*n-5)<<1+isprime(6*n-1) \\ M. F. Hasler, Jun 16 2008

Crossrefs

Cf. A002476, A007528.

Sequence in context: A172364 A323596 A323375 * A167817 A153401 A181520

Adjacent sequences: A140363 A140364 A140365 * A140367 A140368 A140369

Keyword

nonn

Author

Juri-Stepan Gerasimov, Jun 10 2008

Extensions

Edited by M. F. Hasler, Jun 16 2008

a(61)-a(87) from James C. McMahon, Jul 08 2025

Status

approved