A359097 Number of distinct primes of type k + reverse(k) when k is a (2n - 1)-digit number.

1, 25, 304, 3909, 58299, 907721

Offset: 1

Author

Jean-Marc Rebert, Dec 16 2022

Keywords

• nonn
• base
• more

Examples

			1 + reverse(1) = 2  is prime and for no other 1-digit number k, k + reverse(k) = 2k is prime, thus a(2*1-1) = a(1) = 1.
		

Crossrefs

Cf. A358985, A056964, A067030, A358986.

Programs

PARI

R(k)=fromdigits(Vecrev(digits(k)))
a(n)=my(m=2*n-1,u=Set([]),mmin=10^(m-1),mmax=10^m-1,card=0);for(m=mmin,mmax,y=m+R(m);if(isprime(y)&&!setsearch(u,y),u=Set(concat(u,y));card++));card