A068700 The concatenation of n with n-1 and n with n+1 both yield primes (twin primes).

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

Offset: 1

Author

Amarnath Murthy, Mar 04 2002

Keywords

• base
• nonn

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

Examples

			42 is a member as 4241 as well as 4243 are primes.
		

Links

• Zak Seidov, Table of n, a(n) for n = 1..10000

Crossrefs

Common terms of A030458 and A052089.

Intersection of A030457 and A054211; A102478.

Programs

Haskell

import Data.List.Ordered (isect)
a068700 n = a068700_list !! (n-1)
a068700_list = isect a030457_list a054211_list
-- Reinhard Zumkeller, Jun 27 2015

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 *)

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,",")))

Extensions

More terms from Benoit Cloitre, Mar 09 2002