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A212494 Base 2i representation of nonnegative integers. 5
0, 1, 2, 3, 10300, 10301, 10302, 10303, 10200, 10201, 10202, 10203, 10100, 10101, 10102, 10103, 10000, 10001, 10002, 10003, 20300, 20301, 20302, 20303, 20200, 20201, 20202, 20203, 20100, 20101, 20102, 20103 (list; graph; refs; listen; history; text; internal format)
The use of negabinary dispenses with the need for sign bits and for keeping track of signed and unsigned data types. Similarly, the use of base 2i, or quater-imaginary, dispenses with the need to represent the real and imaginary parts of a complex number separately. (The term "quater-imaginary" appears in Knuth's landmark book on computer programming).
Quater-imaginary, based on the powers of 2i (twice the imaginary unit), uses the digits 0, 1, 2, 3. For purely real positive integers, the quater-imaginary representation is the same as negaquartal (base -4) except that 0's are "riffled" in, corresponding to the odd-indexed powers of 2i which are purely imaginary numbers. Therefore, to obtain the base 2i representations of positive real numbers, the algorithm for base -4 representations can be employed with only a small adjustment.
To obtain the base 2i representation of a complex number a+bi, do as above for the real part, then again for the real part of 2i*(a+bi) = -2b+2ai, giving the digits corresponding to the odd-indexed powers of 2i.
Omitting digits for odd powers of 2i (all 0's for the imaginary parts) (e.g. 20300 --> 230) gives A007608 (nonnegative integers in base -4).
Donald Knuth, The Art of Computer Programming. Volume 2, 2nd Edition. Reading, Massachussetts: Addison-Wesley (1981): 189
Joerg Arndt, Radix 2i
Donald Knuth, An imaginary number system, Communications of the ACM 3 (4), April 1960, pp. 245-247.
a(5) = 10301 because 5 = 1*(2i)^4+3*(2i)^2+1*(2i)^0 = 1*16+3*(-4)+1*1
Cf. A212542 (Base 2i representation of negative integers).
Cf. A177505.
Cf. A007608 (Nonnegative integers in base -4).
Sequence in context: A137078 A146026 A115640 * A197635 A171161 A101445
Daniel Forgues, May 18 2012

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Last modified November 29 07:41 EST 2023. Contains 367429 sequences. (Running on oeis4.)