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 A005351 Base -2 representation for n regarded as base 2, then evaluated. (Formerly M4059) 14
 0, 1, 6, 7, 4, 5, 26, 27, 24, 25, 30, 31, 28, 29, 18, 19, 16, 17, 22, 23, 20, 21, 106, 107, 104, 105, 110, 111, 108, 109, 98, 99, 96, 97, 102, 103, 100, 101, 122, 123, 120, 121, 126, 127, 124, 125, 114, 115, 112, 113, 118, 119, 116, 117, 74, 75, 72, 73, 78, 79, 76 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 COMMENTS a(n) = n when n is a power of 4. This is because the even-indexed powers of 2 are the same as the even-indexed powers of -2. - Alonso del Arte, Feb 09 2012 a(n) = n if n is a sum of distinct powers of 4. - Michael Somos, Aug 27 2012 Write n = Sum_{i in b(n)} (-2)^(i - 1), which uniquely determines the set of positive integers b(n). Then a(n) = Sum_{i in b(n)} 2^(i - 1). For example, a(7) = 27 because 7 = (-2)^0 + (-2)^1 + (-2)^3 + (-2)^4 and 27 = 2^0 + 2^1 + 2^3 + 2^4. - Gus Wiseman, Jul 26 2019 REFERENCES M. Gardner, Knotted Doughnuts and Other Mathematical Entertainments. Freeman, NY, 1986, p. 101. N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence). LINKS Reinhard Zumkeller, Table of n, a(n) for n = 0..8191 Joerg Arndt, Matters Computational (The Fxtbook), p. 58-59 Eric Weisstein's World of Mathematics, Negabinary Wikipedia, Negative base A. Wilks, Email, May 22 1991 FORMULA a(4n+2) = 4a(n+1)+2, a(4n+3) = 4a(n+1)+3, a(4n+4) = 4a(n+1), a(4n+5) = 4a(n+1)+1, n>-2, a(1)=1. - Ralf Stephan, Apr 06 2004 EXAMPLE 2 = 4+(-2)+0 = 110 => 6, 3 = 4+(-2)+1 = 111 => 7, ..., 6 = (16)+(-8)+0+(-2)+0 = 11010 => 26. MATHEMATICA f[n_] := Module[{t = 2(4^Floor[ Log[4, Abs[n] + 1] + 2] - 1)/3}, BitXor[n + t, t]]; Table[ f[n]], {n, 0, 60}] (* Robert G. Wilson v, Jan 24 2005 *) PROG (Haskell) a005351 0 = 0 a005351 n = a005351 n' * 2 + m where    (n', m) = if r < 0 then (q + 1, r + 2) else (q, r)              where (q, r) = quotRem n (negate 2) -- Reinhard Zumkeller, Jul 07 2012 (Python) def A005351(n):     s, q = '', n     while q >= 2 or q < 0:         q, r = divmod(q, -2)         if r < 0:             q += 1             r += 2         s += str(r)     return int(str(q)+s[::-1], 2) # Chai Wah Wu, Apr 10 2016 CROSSREFS Cf. A039724. Complement of A005352. Cf. A185269. - Jonathan Vos Post, Feb 19 2011 Cf. A000120, A029931, A035327, A053985, A065359, A070939, A326032. Sequence in context: A019932 A004447 A258989 * A098882 A254374 A019616 Adjacent sequences:  A005348 A005349 A005350 * A005352 A005353 A005354 KEYWORD nonn,base,easy,nice,look AUTHOR EXTENSIONS More terms from Robert G. Wilson v, Jan 24 2005 STATUS approved

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Last modified October 13 18:57 EDT 2019. Contains 327981 sequences. (Running on oeis4.)