A176597 - OEIS

%I #41 Apr 23 2024 07:16:50

%S 22,33,55,77,1111,1313,1717,1919,2323,2929,3131,3737,4141,4343,4747,

%T 5353,5959,6161,6767,7171,7373,7979,8383,8989,9797,101101,103103,

%U 107107,109109,113113,127127,131131,137137,139139,149149,151151,157157,163163

%N Double primes: concatenation of the n-th prime with itself.

%H Vincenzo Librandi, <a href="/A176597/b176597.txt">Table of n, a(n) for n = 1..1000</a>

%e Concatenation 2 and 2 is 22; 3 and 3 is 33; 5 and 5 is 55; etc.

%t dp[n_] := Module[{idn = IntegerDigits[n]}, FromDigits[Join[idn, idn]]]; dp /@ Prime[Range[40]] (* _Harvey P. Dale_, Jun 02 2011 *)

%o (Magma) [Seqint(Intseq(p) cat Intseq(p)): p in PrimesUpTo(200)]; // _Vincenzo Librandi_, Mar 14 2013

%o (PARI) a(n) = { my(p=Str(prime(n))); eval(concat(p,p)); } /* _Joerg Arndt_, Mar 14 2013 */

%Y Cf. A000040, A020338, A067087.

%K nonn,base

%O 1,1

%A _Vincenzo Librandi_, Apr 21 2010

%E Edited by _Charles R Greathouse IV_ and _R. J. Mathar_, Apr 23 2010