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A260802 Odd numbers x = 2n - 1 such that the concatenation of A019519(n) and A038395(n-1) is prime. 0
3, 13, 19, 21, 67 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Table of n, a(n) for n=1..5.

EXAMPLE

a(1) = 3 since 13_1 is prime;

a(2) = 13 since 135791113_1197531 is prime;

a(3) = 19 since 135791113151719_1715131197531 is prime.

PROG

(Python)

import sympy

n=1

while n>0:

....s=str(n)

....for m in range(n-2, 0, -2):

........s=str(m)+s+str(m)

....p=int(s)

....if sympy.isprime(p)==True:

........print(n)

....n=n+2

CROSSREFS

Cf. A019519, A038395.

Sequence in context: A024474 A024599 A071600 * A045435 A038974 A168425

Adjacent sequences:  A260799 A260800 A260801 * A260803 A260804 A260805

KEYWORD

nonn,more,base

AUTHOR

Abhiram R Devesh, Jul 31 2015

STATUS

approved

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Last modified September 23 22:32 EDT 2020. Contains 337315 sequences. (Running on oeis4.)