|
|
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
|
|
LINKS
|
|
|
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:
|
|
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
|
|
CROSSREFS
|
|
|
KEYWORD
|
base,nonn
|
|
AUTHOR
|
|
|
EXTENSIONS
|
|
|
STATUS
|
approved
|
|
|
|