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A102478
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Numbers n such that the concatenations (2*n),(2*n-1) and (2*n),(2*n+1) give twin primes.
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1
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21, 39, 51, 54, 90, 96, 135, 150, 156, 165, 171, 195, 210, 261, 270, 306, 330, 411, 420, 441, 501, 570, 615, 636, 741, 771, 816, 885, 1050, 1095, 1341, 1371, 1536, 1599, 1704, 1821, 1914, 2121, 2226, 2286, 2370, 2394, 2499, 2811, 2859, 2916, 3051, 3129, 3714
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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LINKS
| Harvey P. Dale, Table of n, a(n) for n = 1..8000
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EXAMPLE
| 2*21=42, 4241 and 4243 are twin primes so a(1)=21
2*39=78, 7877 and 7879 are twin primes so a(2)=39
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MATHEMATICA
| concatQ[n_]:=Module[{idn=IntegerDigits[2n], concatidn}, concatidn=FromDigits[Join[idn, idn]]; And@@PrimeQ[{concatidn-1, concatidn+1}]]; Select[Range[4000], concatQ] (* From Harvey P. Dale, Feb 07 2012 *)
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CROSSREFS
| Sequence in context: A139768 A176071 A072708 * A020220 A084856 A070666
Adjacent sequences: A102475 A102476 A102477 * A102479 A102480 A102481
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KEYWORD
| nonn,base,changed
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AUTHOR
| Pierre CAMI (pierre-cami(AT)bbox.fr), Feb 24 2005
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EXTENSIONS
| Edited by Charles R Greathouse IV (charles.greathouse(AT)case.edu), Apr 29 2010
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