A279213 - OEIS

%I #19 Dec 16 2024 14:37:18

%S 41,107,1613,2017,3229,4441,4643,5653,7673,9491,106103,116113,124121,

%T 130127,136133,170167,172169,182179,184181,196193,206203,212209,

%U 214211,220217,224221,230227,272269,274271,280277,302299,304301,320317,322319,326323,334331

%N Primes formed by concatenating n with n-3.

%H Indranil Ghosh, <a href="/A279213/b279213.txt">Table of n, a(n) for n = 1..10000</a>

%e 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 Select[Table[FromDigits[Join[Flatten[IntegerDigits[{n, n -3}]]]], {n, 400}], PrimeQ]

%o (Magma) [m: n in [4..400 by 2] | IsPrime(m) where m is Seqint(Intseq(n-3) cat Intseq(n))];

%o (Python)

%o from sympy import isprime

%o i=4

%o j=1

%o while j<=10000:

%o     if isprime(int(str(i)+str(i-3)))==True:

%o         print(str(j)+" "+str(i)+str(i-3))

%o         j+=1

%o     i+=1 # _Indranil Ghosh_, Jan 23 2017

%o (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 /* Print initial 35 terms as follows: */

%o terms(35) \\ _Felix Fröhlich_, Jan 23 2017

%Y Cf. A052089, A104332.

%K nonn,base

%O 1,1

%A _Vincenzo Librandi_, Dec 08 2016