OFFSET
1,1
COMMENTS
Primes in A309809.
LINKS
Robert Israel, Table of n, a(n) for n = 1..10000
EXAMPLE
a(3)=613 is the concatenation of 6 and 2*6+1=13 and is prime.
MAPLE
select(isprime, [seq(n*10^(1+ilog10(2*n+1))+2*n+1, n=1..200)]);
PROG
(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
CROSSREFS
KEYWORD
nonn,base
AUTHOR
J. M. Bergot and Robert Israel, Aug 17 2019
STATUS
approved