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A212526 Negative integers in base -4. 6
13, 12, 11, 10, 23, 22, 21, 20, 33, 32, 31, 30, 1303, 1302, 1301, 1300, 1313, 1312, 1311, 1310, 1323, 1322, 1321, 1320, 1333, 1332, 1331, 1330, 1203, 1202, 1201, 1200, 1213, 1212, 1211, 1210, 1223, 1222, 1221, 1220 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Interleaving with zeros gives A212542 (base 2i representation of negative integers).

More precisely, a(n) is the representation of -n in base -4. - M. F. Hasler, May 21 2012

LINKS

Joerg Arndt, Table of n, a(n) for n = 1..1000

EXAMPLE

a(13)=1303:  1*(-4)^3 + 3*(-4)^2 + 0*(-4)^1 + 3*(-4)^0 = -64 + 48 +3 = -13.

MAPLE

a:= proc(n) local d, i, l, m;

      m:= n;

      l:= NULL;

      for i from 0 while m>0 do

        d:= irem(m, 4, 'm');

        if irem (i, 2)=0 and d>0 then d:= 4-d; m:= m+1 fi;

        l:= d, l

      od; parse(cat(l))

    end:

seq(a(n), n=1..60);  # Alois P. Heinz, May 20 2012

PROG

(PARI) A212526(n, s="")={n=-n; until(!n\=-4, s=Str(n%-4, s)); eval(s)}  \\ M. F. Hasler, May 21 2012

(Python)

def A212526(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 10 2016

CROSSREFS

Cf. A007608 (Nonnegative integers in base -4).

Sequence in context: A022969 A023455 A055124 * A019331 A004454 A113548

Adjacent sequences:  A212523 A212524 A212525 * A212527 A212528 A212529

KEYWORD

nonn,base

AUTHOR

Joerg Arndt, May 20 2012

STATUS

approved

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Last modified November 14 01:24 EST 2019. Contains 329108 sequences. (Running on oeis4.)