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A052089 Primes formed by concatenating n with n-1. 27


%S 43,109,2221,2423,3433,4241,5857,7069,7877,8887,10099,102101,108107,

%T 112111,114113,124123,148147,154153,160159,172171,180179,192191,

%U 198197,202201,208207,210209,214213,238237,244243,262261,264263,268267,270269

%N Primes formed by concatenating n with n-1.

%H Paul Tek, <a href="/A052089/b052089.txt">Table of n, a(n) for n = 1..10000</a>

%e 2423 is a prime and a concatenation of 24 and 23.

%t Sort[Select[FromDigits[Flatten[IntegerDigits/@#]]&/@Partition[ Range[ 300,1,-1],2,1],PrimeQ]] (* _Harvey P. Dale_, May 09 2012 *)

%o (PARI) for(n=4,1e4,if(isprime(t=eval(Str(n,n-1))),print1(t", "))) \\ _Charles R Greathouse IV_, May 07 2013

%o (MAGMA) [Seqint(Intseq(n-1) cat Intseq(n)): n in [2..300 by 2] | IsPrime(Seqint(Intseq(n-1) cat Intseq(n)))]; // _Marius A. Burtea_, Mar 21 2019

%Y Cf. A030458, A052087, A052088.

%K nonn,base

%O 1,1

%A _Patrick De Geest_, Jan 15 2000

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Last modified January 16 09:13 EST 2021. Contains 340204 sequences. (Running on oeis4.)