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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)
 OFFSET 0,3 COMMENTS 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 0s 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). REFERENCES Donald Knuth, The Art of Computer Programming. Volume 2, 2nd Edition. Reading, Massachussetts: Addison-Wesley (1981): 189 LINKS Joerg Arndt, Table of n, a(n) for n = 0..1000 Joerg Arndt, Radix 2i Donald Knuth, An imaginary number system, Communications of the ACM 3 (4), April 1960, pp. 245-247. OEIS Wiki, Quater-imaginary base Wikipedia, Quater-imaginary base EXAMPLE a(5) = 10301 because 5 = 1*(2i)^4+3*(2i)^2+1*(2i)^0 = 1*16+3*(-4)+1*1 CROSSREFS 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 Adjacent sequences:  A212491 A212492 A212493 * A212495 A212496 A212497 KEYWORD nonn,base AUTHOR Daniel Forgues, May 18 2012 STATUS approved

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