A380785 Smallest of two consecutive primes p and q, both ending with 1, such that q - p = 10n, or -1 if no such primes exist.

181, 13421, 4831, 25261, 95651, 43331, 175141, 1060781, 404851, 1648081, 2597981, 6085441, 22151281, 10270451, 25180321, 79817581, 84549821, 135045091, 306099181, 529811591, 164710681, 707429491, 965524181, 391995431, 428045491, 1516828721, 4272226951, 2337682591

Offset: 1

Author

Jean-Marc Rebert, Feb 03 2025

Keywords

• nonn
• base

Examples

			a(1) = 181, because 181 and 181 + 10 = 191 are two consecutive primes with the same last digit 1 and no smaller p has this property.
		

Crossrefs

Cf. A054681, A140791.

Programs

PARI

a(n) = my(p=11); while (!isprime(p) || ((nextprime(p+1)-p) != 10*n), p+=10); p; \\ Michel Marcus, Feb 20 2025