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 A053985 Replace 2^k with (-2)^k in binary expansion of n. 18
 0, 1, -2, -1, 4, 5, 2, 3, -8, -7, -10, -9, -4, -3, -6, -5, 16, 17, 14, 15, 20, 21, 18, 19, 8, 9, 6, 7, 12, 13, 10, 11, -32, -31, -34, -33, -28, -27, -30, -29, -40, -39, -42, -41, -36, -35, -38, -37, -16, -15, -18, -17, -12, -11, -14, -13, -24, -23, -26, -25, -20, -19 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 COMMENTS Base 2 representation for n (in lexicographic order) converted from base -2 to base 10. Maps natural numbers uniquely onto integers; within each group of positive values, maximum is in A002450; a(n)=n iff n can be written only with 1's and 0's in base 4 (A000695) a(n) = A004514(n) - n. - Reinhard Zumkeller, Dec 27 2003 LINKS Rémy Sigrist, Table of n, a(n) for n = 0..8191 R. Stephan, Some divide-and-conquer sequences ... R. Stephan, Table of generating functions FORMULA From Ralf Stephan, Jun 13 2003: (Start) G.f.: (1/(1-x)) * Sum_{k>=0} (-2)^k*x^2^k/(1+x^2^k). a(0) = 0, a(2n) = -2a(n), a(2n+1) = -2a(n)+1. (End) a(n) = Sum_{k>=0} A030308(n,k)*A122803(k). - Philippe Deléham, Oct 15 2011 EXAMPLE a(9)=-7 because 9 is written 1001 base 2 and (-2)^3 + (-2)^0 = -8 + 1 = -7. MATHEMATICA f[n_Integer, b_Integer] := Block[{l = IntegerDigits[n]}, Sum[l[[ -i]]*(-b)^(i - 1), {i, 1, Length[l]}]]; a = Table[ FromDigits[ IntegerDigits[n, 2]], {n, 0, 80}]; b = {}; Do[b = Append[b, f[a[[n]], 2]], {n, 1, 80}]; b PROG (PARI) a(n) = fromdigits(binary(n), -2) \\ Rémy Sigrist, Sep 01 2018 CROSSREFS Inverse of A005351. Cf. A039724, A007088, A065369, A073791, A073792, A073793, A073794, A073795, A073796 and A073835. Sequence in context: A163509 A161399 A318479 * A091564 A321301 A191379 Adjacent sequences:  A053982 A053983 A053984 * A053986 A053987 A053988 KEYWORD base,easy,sign AUTHOR Henry Bottomley, Apr 03 2000 STATUS approved

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Last modified June 6 04:15 EDT 2020. Contains 334859 sequences. (Running on oeis4.)