A120825 a(n) consecutive digits ascending beginning with the digit 7 give a prime.

1, 5, 15, 51, 8411

Offset: 1

Author

Robert G. Wilson v, Jul 05 2006

Keywords

• nonn
• base
• hard
• more

Comments

Digits are in ascending order beginning with 7 and after 9 comes 0.

The sequence "a(n) consecutive digits descending beginning with the digit 7 give a prime" has only two terms below 6001, namely 1 and 5, which represent the primes 7 and 76543, respectively.

a(6) >= 100000. - Michael S. Branicky, Apr 07 2025

Examples

			1 is here because 7 is prime.
5 is here because 78901 is prime.
15 is here because 789012345678901 is a prime.
51 is here because 789012345678901234567890123456789012345678901234567 is prime.
		

Crossrefs

Cf. A006055, A120819, A120820, A120821, A120822, A120823, A120824, A120826, A120827.

Programs

Mathematica

fQ[n_] := PrimeQ@ FromDigits@ Mod[6+Range@n, 10]; lst = {}; Do[ If[fQ@n, AppendTo[lst, n]; Print@n], {n, 5000}]; lst

Extensions

a(5) from Bert Dobbelaere, Apr 01 2025