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 A068700 The concatenation of n with n-1 and n with n+1 both yield primes (twin primes). 4
 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 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS All terms are congruent to {0, 12, 18} mod 30. - Zak Seidov, Oct 24 2014 a(n) = 2 * A102478(n). - Reinhard Zumkeller, Jun 27 2015 LINKS Zak Seidov, Table of n, a(n) for n = 1..10000 EXAMPLE 42 is a member as 4241 as well as 4243 are primes. MAPLE filter:= proc(n) local d; d:= ilog10(n)+1; isprime(n*10^d+n-1) and isprime(n*10^d+n+1) end proc: select(filter, [\$1..10^5]); # Robert Israel, Oct 24 2014 MATHEMATICA 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 *) PROG (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 -- Reinhard Zumkeller, Jun 27 2015 CROSSREFS Common terms of A030458 and A052089. Intersection of A030457 and A054211; A102478. Sequence in context: A259737 A039525 A072326 * A303283 A135850 A250381 Adjacent sequences: A068697 A068698 A068699 * A068701 A068702 A068703 KEYWORD base,nonn AUTHOR Amarnath Murthy, Mar 04 2002 EXTENSIONS More terms from Benoit Cloitre, Mar 09 2002 STATUS approved

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Last modified August 10 16:53 EDT 2024. Contains 375058 sequences. (Running on oeis4.)