1,1

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

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

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

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

(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

Cf. A019519, A038395.

Sequence in context: A024474 A024599 A071600 * A045435 A038974 A168425

Adjacent sequences: A260799 A260800 A260801 * A260803 A260804 A260805

nonn,more,base

Abhiram R Devesh, Jul 31 2015

approved