A120828 Numbers k such that the concatenation of n successive descending digits (1,0,9,8,7,...) starting with 1 is prime.

3, 5, 35, 139, 153, 253, 1053, 2015, 3703, 6933, 8173, 11959

Offset

1,1

Comments

Digits are in descending order beginning with 1 and after 0 comes 9.

Terms must end in 3, 5 or 9. - Michael S. Branicky, May 11 2023

Links

Table of n, a(n) for n=1..12.

Example

5 is a term since 10987 is a prime.

Maple

filter:= proc(n) local i; isprime( add(10^(n-1-i)*(1-i mod 10), i=0..n-1)) end proc:
select(filter, [$1..4000]); # Robert Israel, Mar 08 2023

Mathematica

fQ[n_] := PrimeQ@ FromDigits@ Mod[2-Range@n, 10]; lst = {}; Do[ If[fQ@n, AppendTo[lst, n]; Print@n], {n, 6000}]; lst

Crossrefs

Cf. A120804, A120819, A120829.

Sequence in context: A001790 A173092 A057908 * A077784 A325582 A145640

Adjacent sequences: A120825 A120826 A120827 * A120829 A120830 A120831

Keyword

nonn,base,hard,more

Author

Robert G. Wilson v, Jul 05 2006

Extensions

Name corrected by Robert Israel, Mar 08 2023

a(10)-a(12) from Michael S. Branicky, May 11 2023

Status

approved