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A182265
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Number of primes p < 10^n such that 4*p+1 is also prime.
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4
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2, 9, 31, 176, 1057, 7422, 53709, 407198, 3198946, 25773602, 212205881, 1777532673
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OFFSET
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1,1
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LINKS
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Table of n, a(n) for n=1..12.
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MATHEMATICA
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f[n_] := Length[Select[Range[10^n], PrimeQ[#] && PrimeQ[4#+1]&]]; Table[f[n], {n, 7}]
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PROG
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(PARI) a(n)=my(s=0); forprime(p=2, 10^n, s+=isprime(4*p+1)); s \\ Charles R Greathouse IV, Apr 23 2012
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CROSSREFS
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Cf. A023212, A092816.
Sequence in context: A150911 A150912 A165653 * A212873 A109770 A242512
Adjacent sequences: A182262 A182263 A182264 * A182266 A182267 A182268
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KEYWORD
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nonn
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AUTHOR
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Enrique Pérez Herrero, Apr 22 2012
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EXTENSIONS
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a(10)-a(12) from Charles R Greathouse IV, Apr 23 2012
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STATUS
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approved
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