The OEIS is supported by the many generous donors to the OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A244862 List of pairs of prime numbers (p,q) starting with (2, 3) such that p || q (where || denotes concatenation) is a prime number and the sequence is always extended with the smallest prime not yet present in the sequence. 2
 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, 331, 281, 317, 283, 397, 293, 311, 307, 337, 313, 373, 347, 359, 349, 379, 353 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS Paolo P. Lava, Table of n, a(n) for n = 1..1000 EXAMPLE The first few pairs are (2,3),(5,23),(7,19),(11,17),(13,61),(29,53), ..., giving the primes 23, 523, 719, 1117, 1361, 2953, ... 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: [I have been informed that this program may be incorrect. - N. J. A. Sloane, Jul 03 2024] # alternative version P:=proc(q) local a, b, k, i, j, n, ok; a:=[2, 3]; for n from 1 to q do k:=3; ok:=1; for i do if ok=1 then k:=nextprime(k); if numboccur(k, a)=0 then b:=k; for j from k do k:=nextprime(k); if numboccur(k, a)=0 then if isprime(b*10^length(k)+k) then a:=[op(a), b, k]; ok:=0; break; fi; fi; od; fi; else break; fi; od; od; print(op(a)); end: P(500); # Paolo P. Lava, Jul 03 2024 CROSSREFS Cf. A000040, A105184. A373794 is a very similar sequence (they first differ at term 69). Sequence in context: A339228 A013639 A047995 * A373794 A338403 A024782 Adjacent sequences: A244859 A244860 A244861 * A244863 A244864 A244865 KEYWORD nonn,base,tabf AUTHOR Michel Lagneau, Jul 25 2014 EXTENSIONS Edited by N. J. A. Sloane, Jul 03 2024. More than the usual number of terms are shown in order to distinguish this from A373794. STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified July 24 21:09 EDT 2024. Contains 374585 sequences. (Running on oeis4.)