A007608 Nonnegative integers in base -4. (Formerly M0926)

0, 1, 2, 3, 130, 131, 132, 133, 120, 121, 122, 123, 110, 111, 112, 113, 100, 101, 102, 103, 230, 231, 232, 233, 220, 221, 222, 223, 210, 211, 212, 213, 200, 201, 202, 203, 330, 331, 332, 333, 320, 321, 322, 323, 310, 311, 312, 313, 300, 301, 302, 303, 13030

Offset

0,3

Comments

The base 2i representation (quater-imaginary representation) of nonnegative integers is obtained by interleaving with zeros, cf. A212494.

More precisely, a(n) is the number n written in base -4; numbers [which represent some nonnegative integer] in base -4 are 0, 1, 2, 3, 100, 101, 102, 103, 110, 111, 112, 113, 120, 121, 122, 123, 130, 131, 132, 133, ... (A212556) - M. F. Hasler, May 20 2012

References

D. E. Knuth, The Art of Computer Programming. Addison-Wesley, Reading, MA, 1969, Vol. 2, p. 189.

N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

Links

Joerg Arndt, Table of n, a(n) for n = 0..1000

Matthew Szudzik, A Mathematica programming contest

Eric Weisstein's World of Mathematics, Negabinary

Wikipedia, Negative base

Mathematica

ToNegaBases[i_Integer, b_Integer] := FromDigits[ Rest[ Reverse[ Mod[ NestWhileList[(#1 - Mod[ #1, b])/-b &, i, #1 != 0 &], b]]]]; Table[ ToNegaBases[n, 4], {n, 0, 55}]

Prog

(PARI) A007608(n, s="")={until(!n\=-4, s=Str(n%-4, s)); eval(s)}  \\ M. F. Hasler, May 20 2012
(Haskell)
a007608 0 = 0
a007608 n = a007608 n' * 10 + m where
   (n', m) = if r < 0 then (q + 1, r + 4) else (q, r)
             where (q, r) = quotRem n (negate 4)
-- Reinhard Zumkeller, Jul 15 2012
(Python)
def A007608(n):
    s, q = '', n
    while q >= 4 or q < 0:
        q, r = divmod(q, -4)
        if r < 0:
            q += 1
            r += 4
        s += str(r)
    return int(str(q)+s[::-1]) # Chai Wah Wu, Apr 09 2016

Crossrefs

Cf. A212556 (sorted), A066323 (sum of digits), A212526 (negative integers in base -4).

Other bases: A007090, A039724, A073785, A073786, A073787, A073788, A073789, A073790 & A039723.

Sequence in context: A006286 A371230 A139129 * A010343 A118169 A066908

Adjacent sequences: A007605 A007606 A007607 * A007609 A007610 A007611

Keyword

base,nice,easy,nonn

Author

N. J. A. Sloane, Robert G. Wilson v, Mira Bernstein

Status

approved