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%I #25 Feb 13 2019 04:57:00
%S 2,3,3,5,61,1171241,1197631,25451791,25451791,9560914721,9560914721,
%T 860964705721,185133795875771
%N a(n) = beginning of a run of at least n primes when x -> 3*x - 2 is iterated.
%C For n > 4, a(n) == 1 (mod 10).
%e a(4) = 5 because 5 is the beginning of 4 primes in succession: 5, 3*5 - 2 = 13 is prime, 3*13 - 2 = 37 is prime, 3*37 - 2 = 109 is prime.
%t c[p_] := Block[{k=1, q = 3 p - 2}, While[PrimeQ[q], q = 3 q - 2; k++]; k]; a[n_] := Block[{p=2}, While[c[p] < n, p = NextPrime[p]]; p]; Array[a, 7]
%o (PARI) a(n)={x=1;k=1;while(k==1,m=0;y=x;while(isprime(y),m++;if(m==n,k=x);y=3*y-2);x++);k;}
%Y Cf. A083388.
%K nonn,more
%O 1,1
%A _Jinyuan Wang_, Jan 25 2019
%E a(8)-a(11) from _Daniel Suteu_, Jan 27 2019
%E a(12)-a(13) from _Giovanni Resta_, Feb 04 2019
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