A260802 Odd numbers x = 2n - 1 such that the concatenation of A019519(n) and A038395(n-1) is prime.

3, 13, 19, 21, 67

Offset: 1

Author

Abhiram R Devesh, Jul 31 2015

Keywords

• nonn
• more
• base

Examples

			a(1) = 3 since 13_1 is prime;
a(2) = 13 since 135791113_1197531 is prime;
a(3) = 19 since 135791113151719_1715131197531 is prime.
		

Crossrefs

Cf. A019519, A038395.

Programs

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