A210514 Prime numbers generated by concatenating k, k, and 9.

229, 449, 11119, 14149, 22229, 28289, 31319, 37379, 44449, 49499, 52529, 56569, 67679, 70709, 71719, 80809, 86869, 89899, 94949, 95959, 1061069, 1101109, 1131139, 1151159, 1161169, 1191199, 1241249, 1251259, 1331339, 1401409, 1431439, 1481489, 1571579, 1601609

Offset

1,1

Comments

This series is similar to A030458 and A052089.

Base considered is 10.

Links

Michael S. Branicky, Table of n, a(n) for n = 1..10000

Example

For k=2, a(1)= 229.
For k=4, a(2)= 449.
For k=11, a(3)= 11119.
For k=14, a(4)= 14149.

Mathematica

Select[Table[FromDigits[Flatten[Join[IntegerDigits/@{n, n}, {9}]]], {n, 200}], PrimeQ] (* Harvey P. Dale, Apr 23 2015 *)

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, 2000):
    p1=int(str(i)+str(i)+"1")
    if len(factors(p1))<3:
        print(p1, end=', ')
(Python)
from sympy import isprime
from itertools import count, islice
def agen(): yield from filter(isprime, (int(str(k)+str(k)+'9') for k in count(1)))
print(list(islice(agen(), 34))) # Michael S. Branicky, Jul 26 2022

Crossrefs

Cf. A030458, A052089.

Sequence in context: A139512 A142263 A142608 * A142665 A124684 A332740

Adjacent sequences: A210511 A210512 A210513 * A210515 A210516 A210517

Keyword

base,nonn,easy

Author

Abhiram R Devesh, Jan 26 2013

Extensions

a(27) and beyond from Michael S. Branicky, Jul 26 2022

Status

approved