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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
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
Sequence in context: A193492 A279204 A091332 * A122043 A179913 A161868
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.)