A088423 - OEIS

A088423

a(n) is the number of primes in arithmetic progression starting with 11 and with d = 2n.

2, 1, 4, 2, 1, 2, 1, 1, 3, 2, 1, 1, 2, 1, 5, 2, 1, 3, 1, 1, 2, 1, 1, 3, 2, 1, 1, 2, 1, 6, 2, 1, 1, 2, 1, 2, 1, 1, 3, 1, 1, 1, 2, 1, 4, 2, 1, 2, 2, 1, 2, 1, 1, 1, 1, 1, 1, 2, 1, 3, 1, 1, 4, 2, 1, 1, 1, 1, 2, 2, 1, 1, 2, 1, 1, 2, 1, 2, 1, 1, 2, 1, 1, 3, 2, 1, 1, 1, 1, 2, 2, 1, 4, 2, 1, 1, 1, 1, 1, 2

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OFFSET

1,1

COMMENTS

Arithmetic progression is stopped when next term is not prime. E.g., for n=3, a=4, that is 11,17,23,29 are prime, while next term, 35, is not prime.

LINKS

Michael De Vlieger, Table of n, a(n) for n = 1..10000

MATHEMATICA

bb={}; Do[s=1; Do[If[PrimeQ[11+k*d], s=s+1, bb={bb, s}; Break[]], {k, 10}], {d, 2, 200, 2}]; Flatten[bb]

PROG

(PARI) a(n) = my(p=11, x=p+2*n, i=1); while(1, if(ispseudoprime(x), i++; x=x+2*n, return(i))) \\ Felix Fröhlich, May 28 2021

CROSSREFS