A309808 Primes formed by concatenating k and 2k+1.

13, 37, 613, 919, 1021, 1123, 1327, 1429, 1531, 2143, 2347, 2551, 2857, 3061, 3163, 3469, 3571, 3673, 3877, 4591, 4999, 50101, 56113, 59119, 63127, 70141, 71143, 74149, 78157, 79159, 81163, 88177, 91183, 93187, 95191, 101203, 105211, 106213, 108217, 110221, 113227, 114229

Offset: 1

Author

J. M. Bergot and Robert Israel, Aug 17 2019

Keywords

• nonn
• base

Comments

Primes in A309809.

Examples

			a(3)=613 is the concatenation of 6 and 2*6+1=13 and is prime.
		

Links

• Robert Israel, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A030458, A309809.

Programs

Magma

[a:m in [1..130]|IsPrime(a) where a is 10^(#Intseq(2*m+1))*m+2*m+1]; // Marius A. Burtea, Aug 18 2019

Maple

select(isprime, [seq(n*10^(1+ilog10(2*n+1))+2*n+1,n=1..200)]);