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A244862 Pairs of prime numbers (p,q) starting with a(1)=2 such that p U q (where U denotes concatenation) is a prime number and a(n) is always extended with the smallest available prime not yet present in the sequence. 0
2, 3, 5, 23, 7, 19, 11, 17, 13, 61, 29, 53, 31, 37, 41, 59, 43, 73, 47, 83, 67, 79, 71, 167, 89, 101, 97, 103, 107, 137, 109, 139, 113, 131, 127, 157, 149, 173, 151, 163, 179, 233, 181, 193, 191, 227, 197, 257, 199, 211, 223, 229, 239, 251, 241, 271, 263, 269, 277 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

The first pairs are (2,3),(5,23),(7,19),(11,17),(13,61),(29,53)=> 23, 523, 719, 1117, 1361, 2953, ... are prime numbers.

LINKS

Table of n, a(n) for n=1..59.

MAPLE

with(numtheory):nn:=60:lst:={2, 3}: printf ( "%d %d \n", 2, 3):

   for a from 2 to nn do:

     p:=ithprime(a):ii:=0:

      for b from 1 to nn while(ii=0)do:

        q:=ithprime(b):s:=p*10^(length(q))+q:

         if type(s, prime)=true and lst intersect {p, q}={}

          then

          lst:=lst union {p, q}:ii:=1:printf(`%d, `, p):printf(`%d, `, q):

          else

        fi:

      od:

    od:

CROSSREFS

Cf. A000040, A105184.

Sequence in context: A093499 A013639 A047995 * A024782 A024775 A024767

Adjacent sequences:  A244859 A244860 A244861 * A244863 A244864 A244865

KEYWORD

nonn,base

AUTHOR

Michel Lagneau, Jul 25 2014

STATUS

approved

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Last modified October 14 04:37 EDT 2019. Contains 327995 sequences. (Running on oeis4.)