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 A210515 Numbers N such that concatenation of N, N, and x generates a prime for x=1 and x=3 and x=7 and x=9. 0
 1235, 4061, 8255, 22775, 24665, 36500, 44501, 52343, 54434, 57644, 58109, 59567, 59588, 65018, 69407, 71789, 78689, 94280, 98594, 106748, 114272, 122504, 134369, 137129, 138905, 144302, 162236, 196439, 235808, 238235, 269912, 277919, 278633, 282461, 290534 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS The primes generated are part of the sequences A210511, A210512, A210513 and A210514. LINKS Table of n, a(n) for n=1..35. MATHEMATICA Select[Range[3*10^5], AllTrue[FromDigits/@Table[Join[IntegerDigits[#], IntegerDigits [#], {n}], {n, {1, 3, 7, 9}}], PrimeQ]&] (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, Jul 07 2021 *) PROG (Python) import numpy as np from functools import reduce 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, 50000): p1=int(str(i)+str(i)+"1") p3=int(str(i)+str(i)+"3") p7=int(str(i)+str(i)+"7") p9=int(str(i)+str(i)+"9") if len(factors(p1))<3 and len(factors(p3))<3 and len(factors(p7))<3 and len(factors(p9))<3: print(i, end=', ') CROSSREFS Cf. A210511, A210512, A210513, A210514. Sequence in context: A193492 A279204 A091332 * A122043 A179913 A161868 Adjacent sequences: A210512 A210513 A210514 * A210516 A210517 A210518 KEYWORD base,nonn,easy AUTHOR Abhiram R Devesh, Jan 26 2013 STATUS approved

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Last modified February 25 11:04 EST 2024. Contains 370324 sequences. (Running on oeis4.)