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Search: id:A075134
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| A075134 |
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Indices of triple-safe primes: p=prime(n) is double-safe: q=(p-1)/2, r=(q-1)/2, and s=)r-1)/2 are all prime (and q is double-safe). |
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+0
1
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| 9, 15, 128, 228, 417, 562, 1214, 1364, 2425, 3085, 5281, 8256, 8926, 9187, 9332, 12782, 14497, 14607, 16227, 18763, 19601, 21476, 29911
(list; graph; listen)
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OFFSET
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1,1
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COMMENT
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prime p is safe if q=(p-1)/2 is prime, so p is double safe if also r=(q-1)/2 is prime. So p is triple-safe if q is double safe Safe primes are in A005385, indices of double-safe primes are in A075133
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EXAMPLE
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15 is a member because p(15)=47, q=(p-1)/2=23, r=(q-1)2=11 and s=(r-1)=5 are primes.
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MATHEMATICA
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se3=Select[(Select[(Select[(Prime[Range[30000]]-1)/2, PrimeQ]-1)/2, PrimeQ]-1)/2, PrimeQ]; Map[PrimePi, Map[2(2(2*#+1)+1)+1&, se3]]
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CROSSREFS
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Cf. A005385, A075133.
Sequence in context: A136354 A098146 A124274 this_sequence A100241 A078794 A093595
Adjacent sequences: A075131 A075132 A075133 this_sequence A075135 A075136 A075137
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KEYWORD
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nonn
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AUTHOR
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Zak Seidov (zakseidov(AT)yahoo.com), Sep 04 2002
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