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 A090715 Primes which are also prime if their base 31 representation is interpreted as a base 10 number. 1

%I #13 Nov 21 2013 12:48:16

%S 2,3,5,7,71,127,131,193,251,257,1061,1063,1117,1123,1181,1187,1249,

%T 1987,1993,2111,2917,3041,3109,3169,3853,3907,4099,4967,5023,5087,

%U 5897,5953,6823,6829,6883,6947,7013,7753,7757,7759,7877,7937,8681,8689,8807,8867

%N Primes which are also prime if their base 31 representation is interpreted as a base 10 number.

%H Vincenzo Librandi, <a href="/A090715/b090715.txt">Table of n, a(n) for n = 1..1000</a>

%e 71 is prime; in base 31 it is written "29" and the base 10 number 29 is also prime.

%t b31Q[n_]:=Module[{idn31=IntegerDigits[n,31]},Max[idn31] <10&&PrimeQ[FromDigits[idn31]]]; Select[Prime[Range [PrimePi[9000]]],b31Q] (* _Harvey P. Dale_, Mar 19 2011 *)

%K base,nonn

%O 1,1

%A _Cino Hilliard_, Jan 18 2004

%E Edited by _Jens Kruse Andersen_, May 04 2008

%E Changed offset from 2 to 1 by _Vincenzo Librandi_, Apr 18 2013

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Last modified August 11 14:00 EDT 2024. Contains 375069 sequences. (Running on oeis4.)