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%I #43 Sep 13 2015 05:04:14
%S 2,3,5,23,7,19,11,17,13,61,29,53,31,37,41,59,43,73,47,83,67,79,71,167,
%T 89,101,97,103,107,137,109,139,113,131,127,157,149,173,151,163,179,
%U 233,181,193,191,227,197,257,199,211,223,229,239,251,241,271,263,269,277
%N 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.
%C 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.
%p with(numtheory):nn:=60:lst:={2,3}: printf ( "%d %d \n",2,3):
%p for a from 2 to nn do:
%p p:=ithprime(a):ii:=0:
%p for b from 1 to nn while(ii=0)do:
%p q:=ithprime(b):s:=p*10^(length(q))+q:
%p if type(s,prime)=true and lst intersect {p,q}={}
%p then
%p lst:=lst union {p,q}:ii:=1:printf(`%d, `,p):printf(`%d, `,q):
%p else
%p fi:
%p od:
%p od:
%Y Cf. A000040, A105184.
%K nonn,base
%O 1,1
%A _Michel Lagneau_, Jul 25 2014
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