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A084957
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Initial prime of the first prime chain of length n under the iteration x -> 4x + 3.
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6
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2, 2, 2, 2, 1447, 9769, 17231, 17231, 32611, 18527009, 161205841, 3123824801, 26813406071, 4398156030379, 4398156030379
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OFFSET
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1,1
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COMMENTS
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This is a special case of prime chains generated by f(x) = c*x + d.
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LINKS
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EXAMPLE
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a(3) = 2 since 2, f(2) = 11, and f(11) = 47 are primes when f(x) = 4*x + 3.
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MATHEMATICA
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c[p_] := Block[{k=1, q=4*p+3}, While[ PrimeQ[q], q=4*q+3; k++]; k]; a[n_] := Block[ {p=2}, While[c[p] < n, p = NextPrime@ p]; p]; Array[a, 9] (* Giovanni Resta, Mar 21 2017 *)
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PROG
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(PARI) has(p, n)=for(i=2, n, if(!isprime(p=4*p+3), return(0))); 1
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CROSSREFS
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KEYWORD
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nonn,more
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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