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Search: id:A079155
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| A079155 |
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The number of primes less than 10^n whose digital root (A038194) is also prime |
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+0
1
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OFFSET
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1,1
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EXAMPLE
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a(2) = 15 because the only primes less than 100 whose have digital roots are also prime are {2,3,5,7,11,23,29,41,43,47,59,61,79,83,97}.
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MATHEMATICA
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c = 0; k = 1; Do[ While[ k < 10^n, If[ PrimeQ[k] && PrimeQ[ Mod[k, 9]], c++ ]; k++ ]; Print[c], {n, 1, 8}]
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CROSSREFS
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The primes are in A078403, their digital roots are in A078400.
Sequence in context: A130679 A107874 A034496 this_sequence A076900 A081011 A008829
Adjacent sequences: A079152 A079153 A079154 this_sequence A079156 A079157 A079158
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KEYWORD
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base,nonn
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AUTHOR
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Robert G. Wilson v (rgwv(AT)rgwv.com), Dec 27 2002
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