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A154967
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Nonprime numbers n such that concatenation of n and n-th prime is composite.
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1
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1, 8, 9, 10, 14, 15, 16, 20, 21, 22, 24, 25, 26, 28, 32, 33, 34, 38, 39, 40, 44, 48, 49, 50, 51, 52, 55, 60, 62, 63, 64, 65, 66, 68, 69, 70, 72, 74, 75, 76, 77, 78, 80, 81, 84, 86, 87, 88, 90, 91, 94, 95, 96, 98, 100, 102, 104, 105, 106, 108, 110, 111, 112, 114, 116, 118
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OFFSET
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1,2
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LINKS
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EXAMPLE
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The concatenation of the nonprime 1 and the first prime 2 is the composite 12, hence 1 is in the sequence.
Concatenation of nonprime 9 and ninth prime 23 is the composite 923 = 13*71, hence 9 is in the sequence.
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MATHEMATICA
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Select[Range[120], !PrimeQ[#]&&CompositeQ[FromDigits[Join[ IntegerDigits[ #], IntegerDigits[ Prime[#]]]]]&] (* Harvey P. Dale, Mar 08 2018 *)
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PROG
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(Magma) [ n: n in [1..118] | not IsPrime(n) and not IsPrime(StringToInteger(IntegerToString(n) cat IntegerToString(NthPrime(n)))) ];
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CROSSREFS
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KEYWORD
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nonn,base,easy,less
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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