A122587 - OEIS

%I #14 Jan 30 2023 10:59:46

%S 1,2,3,1,1,1,1,2,2,2,2,3,3,3,3,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,2,2,2,

%T 2,2,2,2,2,2,2,2,2,2,2,2,2,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,1,1,1,1,1,

%U 1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1

%N Leading digit of n in base 4.

%C Digits 1, 2 and 3 appear cyclically and each time in runs whose lengths are the powers of 4.

%F a(n) = floor(n/(4^floor(log[4](n)))).

%e a(1) = 1/(4^0) = 1.

%p seq( evalf(floor(n/ (4^floor(log[4](n))))), n=1..500);

%t Table[First[IntegerDigits[n, 4]], {n, 100}] (* _Alonso del Arte_, Sep 30 2011 *)

%o (Python)

%o def A122587(n): return int(bin(n)[2:3+(n.bit_length()&1^1)],2) # _Chai Wah Wu_, Jan 30 2023

%K easy,nonn,base

%O 1,2

%A Peter C. Heinig (algorithms(AT)gmx.de), Oct 20 2006