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A004643 Powers of 2 written in base 4. 13
1, 2, 10, 20, 100, 200, 1000, 2000, 10000, 20000, 100000, 200000, 1000000, 2000000, 10000000, 20000000, 100000000, 200000000, 1000000000, 2000000000, 10000000000, 20000000000, 100000000000, 200000000000 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

COMMENTS

Also seems to be numbers k such that the digits of k^3 are cubes. - Colin Barker, Apr 21 2017

LINKS

Vincenzo Librandi, Table of n, a(n) for n = 0..1000

Index entries for linear recurrences with constant coefficients, signature (0,10).

FORMULA

From Chai Wah Wu, Sep 03 2020: (Start)

a(n) = 10*a(n-2) for n > 1.

G.f.: (-2*x - 1)/(10*x^2 - 1). (End)

a(n) = (3-(-1)^n)/2 * 10^floor(n/2). - Bernard Schott, Sep 17 2020

MATHEMATICA

Table[FromDigits[IntegerDigits[2^n, 4]], {n, 0, 40}] (* Vincenzo Librandi, Jun 07 2013 *)

Table[{1, 2}10^n, {n, 0, 20}]//Flatten (* Harvey P. Dale, Feb 14 2018 *)

PROG

(PARI) for(n=0, 30, print1(fromdigits(digits(2^n, 4)), ", ")) \\ G. C. Greubel, Sep 10 2018

(MAGMA) [Seqint(Intseq(2^n, 4)): n in [0..30]]; // G. C. Greubel, Sep 10 2018

CROSSREFS

Sequence in context: A324474 A294493 A261660 * A284213 A156818 A037422

Adjacent sequences:  A004640 A004641 A004642 * A004644 A004645 A004646

KEYWORD

nonn,base,easy

AUTHOR

N. J. A. Sloane

STATUS

approved

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Last modified September 19 03:31 EDT 2021. Contains 347550 sequences. (Running on oeis4.)