A381511 Smaller of two consecutive primes p and q, both ending with 9, such that q - p = 10*n, or -1 if no such primes exist.

139, 3089, 5749, 20809, 60539, 110359, 173359, 618719, 1294849, 838249, 6877109, 1895359, 11188759, 7621259, 35560009, 33803689, 124956059, 92801029, 142414669, 378043979, 229316459, 390932389, 1095750599, 995151679, 2174082649, 2603726969, 3402493709, 1997191249

Offset: 1

Author

Jean-Marc Rebert, Feb 25 2025

Keywords

• nonn
• base

Examples

			a(1) = 139, because 139 and 139 + 10 = 149 are two consecutive primes with the same last digit 9 and no smaller p has this property.
		

Crossrefs

Cf. A101232, A140791, A380785, A381372. A381510.

Programs

PARI

a(n) = my(p=9); while (!isprime(p) || ((nextprime(p+1)-p) != 10*n), p+=10); p; \\ Michel Marcus, Feb 25 2025

Python

from sympy import isprime, nextprime
def A381511(n):
    p = 19
    while (q:=nextprime(p)):
        if q-p == 10*n:
            return p
        p = q+9-(q%10)
        while not isprime(p):
            p += 10 # Chai Wah Wu, Mar 08 2025