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Numbers k such that the concatenation of n successive descending digits (1,0,9,8,7,...) starting with 1 is prime.
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%I #15 May 13 2023 01:47:23

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

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

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

%C Terms must end in 3, 5 or 9. - _Michael S. Branicky_, May 11 2023

%e 5 is a term since 10987 is a prime.

%p filter:= proc(n) local i; isprime( add(10^(n-1-i)*(1-i mod 10), i=0..n-1)) end proc:

%p select(filter, [$1..4000]); # _Robert Israel_, Mar 08 2023

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

%Y Cf. A120804, A120819, A120829.

%K nonn,base,hard,more

%O 1,1

%A _Robert G. Wilson v_, Jul 05 2006

%E Name corrected by _Robert Israel_, Mar 08 2023

%E a(10)-a(12) from _Michael S. Branicky_, May 11 2023