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A068700
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The concatenation of n with n-1 and n with n+1 both yield primes (twin primes).
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4
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42, 78, 102, 108, 180, 192, 270, 300, 312, 330, 342, 390, 420, 522, 540, 612, 660, 822, 840, 882, 1002, 1140, 1230, 1272, 1482, 1542, 1632, 1770, 2100, 2190, 2682, 2742, 3072, 3198, 3408, 3642, 3828, 4242, 4452, 4572, 4740, 4788, 4998, 5622, 5718, 5832
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listen;
history;
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internal format)
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OFFSET
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1,1
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COMMENTS
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All terms are congruent to {0, 12, 18} mod 30. - Zak Seidov, Oct 24 2014
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LINKS
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EXAMPLE
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42 is a member as 4241 as well as 4243 are primes.
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MAPLE
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filter:= proc(n)
local d;
d:= ilog10(n)+1;
isprime(n*10^d+n-1) and isprime(n*10^d+n+1)
end proc:
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MATHEMATICA
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d[n_]:=IntegerDigits[n]; conQ[n_]:=And@@PrimeQ[FromDigits/@{Join[d[n], d[n+1]], Join[d[n], d[n-1]]}]; Select[Range[5850], conQ[#] &] (* Jayanta Basu, May 21 2013 *)
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PROG
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(PARI) for(n=2, 200, if(isprime(n*10^ceil(log(n-1)/log(10))+n-1)*isprime(n*10^ceil(log(n+1)/log(10))+n+1)==1, print1(n, ", ")))
(Haskell)
import Data.List.Ordered (isect)
a068700 n = a068700_list !! (n-1)
a068700_list = isect a030457_list a054211_list
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CROSSREFS
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KEYWORD
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base,nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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