cp's OEIS Frontend

A028899 Map n = Sum c_i 10^i to a(n) = Sum c_i 4^i.

%I A028899 #12 Jul 08 2025 18:54:46
%S A028899 0,1,2,3,4,5,6,7,8,9,4,5,6,7,8,9,10,11,12,13,8,9,10,11,12,13,14,15,16,
%T A028899 17,12,13,14,15,16,17,18,19,20,21,16,17,18,19,20,21,22,23,24,25,20,21,
%U A028899 22,23,24,25,26,27,28,29,24,25,26,27,28,29,30,31,32,33,28,29,30,31,32,33
%N A028899 Map n = Sum c_i 10^i to a(n) = Sum c_i 4^i.
%H A028899 Robert Israel, <a href="/A028899/b028899.txt">Table of n, a(n) for n = 0..10000</a>
%F A028899 From _Robert Israel_, Jun 11 2018: (Start)
%F A028899 a(i+10*j) = i + 4*a(j) for 0 <= i <= 9.
%F A028899 G.f. g(x) satisfies g(x) = (x+2*x^2+...+9*x^9)/(1-x^10) + 4*(1-x^10)*g(x^10)/(1-x). (End)
%p A028899 f:= proc(n) option remember;
%p A028899 n mod 10 + 4*procname(floor(n/10))
%p A028899 end proc:
%p A028899 f(0):= 0:
%p A028899 map(f, [$0..100]); # _Robert Israel_, Jun 11 2018
%K A028899 nonn,base,look
%O A028899 0,3
%A A028899 _N. J. A. Sloane_
%E A028899 More terms from _Erich Friedman_.