1,2

Where A167020 is the characteristic sequence: A167020(n)=1 iff 6*n-1 is prime.

Table of n, a(n) for n=1..73.

(PARI) ism(n) = isprime(6*n-1); \\ A167020

a(n) = sum(k=1, n, ism(k)); \\ Michel Marcus, Feb 06 2019

Cf. A007528, A167020, A172104.

Sequence in context: A247971 A317334 A331266 * A123731 A247973 A352241

Adjacent sequences: A172100 A172101 A172102 * A172104 A172105 A172106

nonn

Juri-Stepan Gerasimov, Jan 25 2010

Entries checked by R. J. Mathar, Apr 14 2010

approved