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A243886
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Primes p = prime(n): such that p.n and n.p both are prime, where (.) indicates concatenation.
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1
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661, 1051, 1999, 2179, 3433, 3593, 3719, 4073, 4591, 4733, 5449, 5503, 6079, 6481, 7109, 7211, 7489, 8293, 8513, 9901, 10273, 10529, 11821, 12721, 14107, 14591, 14879, 15263, 15877, 18149, 19559, 22027, 22129, 22571, 23339, 24527, 25357, 26881, 27337, 34259
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OFFSET
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1,1
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COMMENTS
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LINKS
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EXAMPLE
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661 is in the sequence because 661 = prime(121): Concatenations of [661.121 = 661121] and concatenation of [121.661 = 121661] which are also primes.
1051 is in the sequence because 1051 = prime(177): Concatenation of [1051.177 = 1051177] and concatenation of [177.1051 = 1771051] which are also primes.
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MAPLE
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with(numtheory): with(StringTools): A243886:= proc() local p, k1, k2; p:=ithprime(n); k1:=parse (cat (p, n)); k2:=parse(cat(n, p)); if isprime(k1)and isprime(k2) then RETURN (p); fi; end: seq(A243886 (), n=1..5000);
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MATHEMATICA
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Select[Prime [Range[5000]], PrimeQ[FromDigits[Join[IntegerDigits [PrimePi [#]], IntegerDigits [#]]]] && PrimeQ [FromDigits [Join [IntegerDigits[#], IntegerDigits [PrimePi [#]]]]] &]
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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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STATUS
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approved
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