login
Primes of the form: (concatenation of first n positive integers) - 1.
1

%I #18 Sep 08 2022 08:46:07

%S 11,123456789101112131415161717

%N Primes of the form: (concatenation of first n positive integers) - 1.

%C Next term, if it exists, has more than 1000 digits.

%e 11 in this sequence because 12-1 is prime.

%t Select[Table[FromDigits[Flatten[IntegerDigits[Range[n]]]] - 1, {n, 1, 100}], PrimeQ] (* after _Bruno Berselli_ *)

%o (Magma) c:=0; for d in [1..3] do m:=10^d; for n in [m div 10..m-1] do c:=c*m+n; t:=c-1; if IsPrime(t) then t; end if; end for; end for; // after _Jon E. Schoenfield_

%Y Cf. A241569.

%K nonn,base,more,bref

%O 1,1

%A _Vincenzo Librandi_, Apr 26 2014