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A088423
a(n) is the number of primes in arithmetic progression starting with 11 and with d = 2n.
10
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
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
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
KEYWORD
easy,nonn
AUTHOR
Zak Seidov, Sep 29 2003
STATUS
approved