A248854 - OEIS

%I #27 Jun 08 2020 12:01:57

%S 1,2,3,16,17,132,1196,11373,110486,1084604,10708554,106091744,

%T 1053422338,10475688326,104287176418,1039019056245,10358018863852,

%U 103307491450819,1030734020030317,10287026204717357,102692313540015923,1025351434864118025,10239531292310798955,102270102190290407385

%N Numbers n such that n - pi(n) is a power of 10.

%C For n > 1 there exist at most two n-digit terms. If n is a term of the sequence and n + 1 is prime then n + 1 is also in the sequence.

%C Numbers n such that pi(n) is equal to n - 10^floor(log(10, n)). - _Farideh Firoozbakht_, Jan 01 2015

%p A[1]:= 1: A[2]:= 2: A[3]:= 3:

%p count:= 3:

%p for k from 1 to 8 do

%p   x:= 10^k; y:= x + numtheory:-pi(x);

%p   while x < y and y < 10^(k+1) do

%p     x:= y; y:= 10^k + numtheory:-pi(x);

%p   od;

%p   count:= count+1; A[count]:= x;

%p   if isprime(x+1) then

%p       count:= count+1; A[count]:= x+1

%p   fi;

%p od:

%p seq(A[i],i=1..count); # _Robert Israel_, Dec 31 2014

%t Select[Range[1000], IntegerQ[Log[10, # - PrimePi[#]]] &] (* _Alonso del Arte_, Jan 01 2015 *)

%o (PARI) for(n=1,10^3,s=digits(n-primepi(n)-1);if(s==[]||vecmin(s)==9,print1(n,", "))) \\ _Derek Orr_, Jan 02 2015

%Y Cf. A000720, A248856, A248857.

%K nonn,hard

%O 1,2

%A _Farideh Firoozbakht_, Dec 31 2014

%E a(19)-a(24) from _Giovanni Resta_, Jun 07 2020