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A210511 Primes formed by concatenating k, k, and 1 for k >= 1.

%I A210511 #36 Jul 26 2022 21:59:03
%S A210511 331,661,881,991,18181,20201,21211,26261,27271,32321,33331,41411,
%T A210511 48481,51511,54541,57571,60601,65651,69691,71711,78781,86861,89891,
%U A210511 90901,92921,98981,99991,1041041,1051051,1131131,1191191,1201201,1221221,1231231,1261261,1281281
%N A210511 Primes formed by concatenating k, k, and 1 for k >= 1.
%C A210511 This sequence is similar to A030458 and A052089.
%H A210511 Vincenzo Librandi, <a href="/A210511/b210511.txt">Table of n, a(n) for n = 1..1000</a>
%t A210511 Select[Table[FromDigits[Flatten[{IntegerDigits[n], IntegerDigits[n], {1}}]], {n, 100}], PrimeQ] (* _Alonso del Arte_, Jan 27 2013 *)
%t A210511 With[{nn=200},Select[FromDigits[Flatten[IntegerDigits[#]]]&/@Thread[ {Range[ nn],Range[nn],1}],PrimeQ]] (* _Harvey P. Dale_, Aug 17 2013 *)
%o A210511 (Python)
%o A210511 import numpy as np
%o A210511 def factors(n):
%o A210511     return reduce(list.__add__, ([i, n//i] for i in range(1, int(n**0.5) + 1) if n % i == 0))
%o A210511 for i in range(1,2000):
%o A210511     p1=int(str(i)+str(i)+"1")
%o A210511     if len(factors(p1))<3:
%o A210511         print(p1)
%o A210511 (Python)
%o A210511 from sympy import isprime
%o A210511 from itertools import count, islice
%o A210511 def agen(): yield from filter(isprime, (int(str(k)+str(k)+'1') for k in count(1)))
%o A210511 print(list(islice(agen(), 36))) # _Michael S. Branicky_, Jul 26 2022
%o A210511 (Magma) [nn1: n in [1..130] | IsPrime(nn1) where nn1 is Seqint([1] cat Intseq(n) cat Intseq(n))]; // _Bruno Berselli_, Jan 30 2013
%Y A210511 Cf. A030458, A052089.
%K A210511 nonn,easy,base
%O A210511 1,1
%A A210511 _Abhiram R Devesh_, Jan 26 2013