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A083388
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a(n) = beginning of a run of at least n primes when x -> 3*x + 2 is iterated.
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9
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2, 3, 5, 29, 1129, 10009, 575119, 32694619, 586130089, 1030544269, 427744892959, 18736892249459, 221530676461709, 221530676461709
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OFFSET
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1,1
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COMMENTS
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LINKS
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EXAMPLE
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a(3) = 5 because 5 is the beginning of 3 primes in succession: 5, 3*5 + 2 = 17 is prime and 3*17 + 2 = 53 is prime.
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MATHEMATICA
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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] (* Giovanni Resta, Mar 21 2017 *)
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PROG
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(PARI) mx=1; forprime(p=1, 198000, x=p; m=0; while(isprime(x=3*x+2), m=m+1; if(m>mx, print(p, " ", m, " ", x); mx=m, ))) \\ Donald S. McDonald, Jun 11 2003
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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