cp's OEIS Frontend

A248854 Numbers n such that n - pi(n) is a power of 10.

%I A248854 #27 Jun 08 2020 12:01:57
%S A248854 1,2,3,16,17,132,1196,11373,110486,1084604,10708554,106091744,
%T A248854 1053422338,10475688326,104287176418,1039019056245,10358018863852,
%U A248854 103307491450819,1030734020030317,10287026204717357,102692313540015923,1025351434864118025,10239531292310798955,102270102190290407385
%N A248854 Numbers n such that n - pi(n) is a power of 10.
%C A248854 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 A248854 Numbers n such that pi(n) is equal to n - 10^floor(log(10, n)). - _Farideh Firoozbakht_, Jan 01 2015
%p A248854 A[1]:= 1: A[2]:= 2: A[3]:= 3:
%p A248854 count:= 3:
%p A248854 for k from 1 to 8 do
%p A248854   x:= 10^k; y:= x + numtheory:-pi(x);
%p A248854   while x < y and y < 10^(k+1) do
%p A248854     x:= y; y:= 10^k + numtheory:-pi(x);
%p A248854   od;
%p A248854   count:= count+1; A[count]:= x;
%p A248854   if isprime(x+1) then
%p A248854       count:= count+1; A[count]:= x+1
%p A248854   fi;
%p A248854 od:
%p A248854 seq(A[i],i=1..count); # _Robert Israel_, Dec 31 2014
%t A248854 Select[Range[1000], IntegerQ[Log[10, # - PrimePi[#]]] &] (* _Alonso del Arte_, Jan 01 2015 *)
%o A248854 (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 A248854 Cf. A000720, A248856, A248857.
%K A248854 nonn,hard
%O A248854 1,2
%A A248854 _Farideh Firoozbakht_, Dec 31 2014
%E A248854 a(19)-a(24) from _Giovanni Resta_, Jun 07 2020