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A088423 a(n) is the number of primes in arithmetic progression starting with 11 and with d = 2n.

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%I A088423 #13 May 29 2021 05:59:51
%S A088423 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,
%T A088423 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,
%U A088423 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
%N A088423 a(n) is the number of primes in arithmetic progression starting with 11 and with d = 2n.
%C A088423 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.
%H A088423 Michael De Vlieger, <a href="/A088423/b088423.txt">Table of n, a(n) for n = 1..10000</a>
%t A088423 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]
%o A088423 (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
%Y A088423 Cf. A088420, A088421, A088422, A088424, A088425, A088426, A088427, A088428, A088429.
%K A088423 easy,nonn
%O A088423 1,1
%A A088423 _Zak Seidov_, Sep 29 2003