A102572 - OEIS

A102572

a(n) = floor(log_4(n)).

0, 0, 0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 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, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3

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OFFSET

1,16

LINKS

Table of n, a(n) for n=1..105.

FORMULA

G.f.: (1/(1 - x))*Sum_{k>=1} x^(4^k). - Ilya Gutkovskiy, Jan 08 2017

PROG

(Magma) [ Ilog(4, n) : n in [1..150] ];

(PARI) a(n)=#digits(n, 4)-1 \\ Twice as fast as a(n)=for(i=0, n, (n>>=2)||return(i)); the naïve code a(n)=log(n)\log(4) works for standard realprecision=28 only up to n=4^47-5 and it is slower by another factor 2. - M. F. Hasler, Mar 11 2015

(PARI) A102572(n)=logint(n, 4) \\ M. F. Hasler, Nov 07 2019

CROSSREFS

Cf. A000523, A062153.

Sequence in context: A356852 A285481 A282622 * A098391 A071702 A225541

Adjacent sequences: A102569 A102570 A102571 * A102573 A102574 A102575

KEYWORD

nonn

AUTHOR

N. J. A. Sloane, Dec 23 2006

STATUS

approved