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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.

%I A381511 #20 Mar 09 2025 12:24:06
%S A381511 139,3089,5749,20809,60539,110359,173359,618719,1294849,838249,
%T A381511 6877109,1895359,11188759,7621259,35560009,33803689,124956059,
%U A381511 92801029,142414669,378043979,229316459,390932389,1095750599,995151679,2174082649,2603726969,3402493709,1997191249
%N 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.
%e A381511 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.
%o A381511 (PARI) a(n) = my(p=9); while (!isprime(p) || ((nextprime(p+1)-p) != 10*n), p+=10); p; \\ _Michel Marcus_, Feb 25 2025
%o A381511 (Python)
%o A381511 from sympy import isprime, nextprime
%o A381511 def A381511(n):
%o A381511     p = 19
%o A381511     while (q:=nextprime(p)):
%o A381511         if q-p == 10*n:
%o A381511             return p
%o A381511         p = q+9-(q%10)
%o A381511         while not isprime(p):
%o A381511             p += 10 # _Chai Wah Wu_, Mar 08 2025
%Y A381511 Cf. A101232, A140791, A380785, A381372. A381510.
%K A381511 nonn,base
%O A381511 1,1
%A A381511 _Jean-Marc Rebert_, Feb 25 2025