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 A084366 Numbers n such that the n-th prime number has an odd number of digits and becomes composite if the central digit is removed. 0
 47, 49, 53, 54, 55, 58, 59, 60, 65, 70, 71, 72, 74, 75, 76, 77, 80, 81, 85, 87, 92, 95, 98, 100, 101, 102, 105, 106, 107, 112, 114, 117, 119, 120, 122, 124, 129, 134, 138, 139, 141, 142, 144, 148, 151, 152, 154, 156, 157, 158, 160, 162, 164, 166, 167 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS Table of n, a(n) for n=1..55. EXAMPLE The 47th prime is 211, omitting the central digit yields 21, which is composite. The 59th prime is 277, omitting the central digit yields 27, which is composite. MATHEMATICA Select[Range[5, 1500], OddQ[Length[IntegerDigits[Prime[ # ]]]] && Not[PrimeQ[FromDigits[Drop[IntegerDigits[Prime[ # ]], {(Length[IntegerDigits[Prime[ # ]]] + 1)/2}]]]] &] ondQ[n_]:=Module[{idn=IntegerDigits[Prime[n]], len}, len=Length[idn]; OddQ[ len] &&CompositeQ[FromDigits[Drop[idn, {(len+1)/2}]]]]; Select[Range[200], ondQ] (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, May 02 2018 *) CROSSREFS Sequence in context: A345502 A249372 A042103 * A257785 A234023 A128940 Adjacent sequences: A084363 A084364 A084365 * A084367 A084368 A084369 KEYWORD base,nonn,less AUTHOR Zak Seidov, Jun 22 2003 EXTENSIONS Edited by Stefan Steinerberger, Sep 05 2007 STATUS approved

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Last modified August 6 02:44 EDT 2024. Contains 374957 sequences. (Running on oeis4.)