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A210511 Primes formed by concatenating n, n, and 1 for n >= 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 series 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

(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 April 7 10:46 EDT 2020. Contains 333301 sequences. (Running on oeis4.)