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

1,1

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 * A338341 A045435 A038974

Adjacent sequences: A260799 A260800 A260801 * A260803 A260804 A260805

Keyword

nonn,more,base

Author

Abhiram R Devesh, Jul 31 2015

Status

approved