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 A210511 Primes formed by concatenating k, k, and 1 for k >= 1. 8
 331, 661, 881, 991, 18181, 20201, 21211, 26261, 27271, 32321, 33331, 41411, 48481, 51511, 54541, 57571, 60601, 65651, 69691, 71711, 78781, 86861, 89891, 90901, 92921, 98981, 99991, 1041041, 1051051, 1131131, 1191191, 1201201, 1221221, 1231231, 1261261, 1281281 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS This sequence is similar to A030458 and A052089. LINKS Vincenzo Librandi, Table of n, a(n) for n = 1..1000 MATHEMATICA Select[Table[FromDigits[Flatten[{IntegerDigits[n], IntegerDigits[n], {1}}]], {n, 100}], PrimeQ] (* Alonso del Arte, Jan 27 2013 *) With[{nn=200}, Select[FromDigits[Flatten[IntegerDigits[#]]]&/@Thread[ {Range[ nn], Range[nn], 1}], PrimeQ]] (* Harvey P. Dale, Aug 17 2013 *) PROG (Python) import numpy as np def factors(n): return reduce(list.__add__, ([i, n//i] for i in range(1, int(n**0.5) + 1) if n % i == 0)) for i in range(1, 2000): p1=int(str(i)+str(i)+"1") if len(factors(p1))<3: print(p1) (Python) from sympy import isprime from itertools import count, islice def agen(): yield from filter(isprime, (int(str(k)+str(k)+'1') for k in count(1))) print(list(islice(agen(), 36))) # Michael S. Branicky, Jul 26 2022 (Magma) [nn1: n in [1..130] | IsPrime(nn1) where nn1 is Seqint([1] cat Intseq(n) cat Intseq(n))]; // Bruno Berselli, Jan 30 2013 CROSSREFS Cf. A030458, A052089. Sequence in context: A020373 A142601 A210534 * A142824 A038647 A152311 Adjacent sequences: A210508 A210509 A210510 * A210512 A210513 A210514 KEYWORD nonn,easy,base AUTHOR Abhiram R Devesh, Jan 26 2013 STATUS approved

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Last modified February 25 11:16 EST 2024. Contains 370325 sequences. (Running on oeis4.)