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A054211
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Numbers k such that k concatenated with k-1 is prime.
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6
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4, 10, 22, 24, 34, 42, 58, 70, 78, 88, 100, 102, 108, 112, 114, 124, 148, 154, 160, 172, 180, 192, 198, 202, 208, 210, 214, 238, 244, 262, 264, 268, 270, 282, 294, 300, 304, 312, 328, 330, 334, 340, 342, 354, 372, 384, 390, 394, 412, 414, 420, 424, 444, 454
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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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MATHEMATICA
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ncpQ[{a_, b_}]:=PrimeQ[FromDigits[Flatten[IntegerDigits[{b, a}]]]]; Transpose[ Select[Partition[Range[500], 2, 1], ncpQ]][[2]] (* Harvey P. Dale, Nov 25 2012 *)
Select[Range[500], PrimeQ[#*10^IntegerLength[#-1]+#-1]&] (* Harvey P. Dale, Mar 16 2019 *)
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PROG
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(Haskell)
a054211 n = a054211_list !! (n-1)
a054211_list = filter ((== 1) . a010051' . a127423) [1..]
(PARI) isok(n) = isprime(eval(Str(n, n-1))); \\ Michel Marcus, Oct 14 2016
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CROSSREFS
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KEYWORD
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nonn,base,nice
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AUTHOR
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STATUS
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approved
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