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A280427
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a(n) is a prime, such that a(n) = p^d-2 where p is a prime and d is the number of digits of p.
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1
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3, 5, 167, 359, 839, 1367, 1847, 2207, 3719, 5039, 7919, 1295027, 3442949, 9393929, 13997519, 21253931, 49430861, 84604517, 95443991, 237176657, 329939369, 384240581, 487443401, 633839777, 904231061, 1078193566319, 1427186233199, 1556727840719, 1985193642959
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OFFSET
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1,1
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COMMENTS
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These numbers (proved for all p < 500) are a subset of A007528. For all even p, such numbers are a subset of A007528. The sequence is a subset of all numbers f(i) such that f(i) = i^d-2 (d - number of digits of integer i) and f(i) is a prime: e.g., f(15) is prime while f(15) = 15^2-2 = 223.
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LINKS
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FORMULA
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a(n) = p^d-2, a(n) is prime, p is a prime and d is the number of digits of p.
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EXAMPLE
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If p=5, then d=1 and a(1)=3; if p=7, then d=1 and a(2)=5; if p=13, then d=2 and a(3)=167; etc.
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MATHEMATICA
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Select[Array[#^IntegerLength@ # - 2 &@ Prime@ # &, 200], PrimeQ] (* Michael De Vlieger, Jan 03 2017 *)
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CROSSREFS
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KEYWORD
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nonn,base
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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