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A279213 Primes formed by concatenating n with n-3.

%I A279213 #19 Dec 16 2024 14:37:18
%S A279213 41,107,1613,2017,3229,4441,4643,5653,7673,9491,106103,116113,124121,
%T A279213 130127,136133,170167,172169,182179,184181,196193,206203,212209,
%U A279213 214211,220217,224221,230227,272269,274271,280277,302299,304301,320317,322319,326323,334331
%N A279213 Primes formed by concatenating n with n-3.
%H A279213 Indranil Ghosh, <a href="/A279213/b279213.txt">Table of n, a(n) for n = 1..10000</a>
%e A279213 For n = 16, n-3 = 13. Concatenating 16 and 13 gives 1613 which is a prime. So, 1613 is in the sequence. - _Indranil Ghosh_, Jan 23 2017
%t A279213 Select[Table[FromDigits[Join[Flatten[IntegerDigits[{n, n -3}]]]], {n, 400}], PrimeQ]
%o A279213 (Magma) [m: n in [4..400 by 2] | IsPrime(m) where m is Seqint(Intseq(n-3) cat Intseq(n))];
%o A279213 (Python)
%o A279213 from sympy import isprime
%o A279213 i=4
%o A279213 j=1
%o A279213 while j<=10000:
%o A279213     if isprime(int(str(i)+str(i-3)))==True:
%o A279213         print(str(j)+" "+str(i)+str(i-3))
%o A279213         j+=1
%o A279213     i+=1 # _Indranil Ghosh_, Jan 23 2017
%o A279213 (PARI) terms(n) = my(i=0, k=3); while(i < n, my(x=eval(Str(k, k-3))); if(ispseudoprime(x), print1(x, ", "); i++); k++)
%o A279213 /* Print initial 35 terms as follows: */
%o A279213 terms(35) \\ _Felix Fröhlich_, Jan 23 2017
%Y A279213 Cf. A052089, A104332.
%K A279213 nonn,base
%O A279213 1,1
%A A279213 _Vincenzo Librandi_, Dec 08 2016