A043452 Numbers having four 7's in base 8.

4095, 8191, 12287, 16383, 20479, 24575, 28671, 29183, 29695, 30207, 30719, 31231, 31743, 32255, 32319, 32383, 32447, 32511, 32575, 32639, 32703, 32711, 32719, 32727, 32735, 32743, 32751, 32759, 32760, 32761, 32762, 32763, 32764, 32765, 32766, 36863, 40959, 45055

Offset: 1

Author

Clark Kimberling

Keywords

• nonn
• base

Links

• Robert Israel, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A007094.

Programs

Maple

G:= proc(x,c,d) local L,m1,m2;
     L:= convert(x,base,7);
     m2:= nops(c);
     m1:= min(nops(L),m2);
     8^d-1 + add((L[i]-7)*8^(c[i]-1),i=1..m1) - 7*add(8^(c[i]-1),i = m1+1..m2)
end proc:
sort([seq(seq(G(x,c,6), x = 0 .. 7^2-1), c=combinat:-choose(6,2))]); # Robert Israel, Sep 24 2017

Mathematica

Select[Range[0, 10^5], DigitCount[#, 8, 7]==4 &] (* Vincenzo Librandi, Sep 25 2017 *)

PARI

isok(n) = #select(x->(x==7), digits(n, 8)) == 4; \\ Michel Marcus, Sep 25 2017