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 A061854 Nondiving binary sequences: numbers which in base 2 have at least the same number of 1's as 0's and reading the binary expansion from left (msb) to right (least significant bit), the number of 0's never exceeds the number of 1's. 8
 1, 2, 3, 5, 6, 7, 10, 11, 12, 13, 14, 15, 21, 22, 23, 25, 26, 27, 28, 29, 30, 31, 42, 43, 44, 45, 46, 47, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 85, 86, 87, 89, 90, 91, 92, 93, 94, 95, 101, 102, 103, 105, 106, 107, 108, 109, 110, 111, 113, 114, 115, 116 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS "msb" = "most significant bit", A053644. These encode lattice walks using steps (+1,+1) (= 1's in binary expansion) and (+1,-1) (= 0's in binary expansion) that start from origin (0,0) and never "dive" under the "sea-level" y=0. The number of such walks of length n (here: the terms of binary width n) is given by C(n,[ n/2 ]) = A001405, which is based on fact mentioned in Guy's article that the shallow diagonals of the Catalan Triangle A009766 sum to A001405. This sequence is a subsequence of A072601. - Jason Kimberley, Feb 08 2013 Define a map from this set onto the nonnegative integers as follows: set the output bit string to be empty representing zero; process the input string from left to right; when 1 occurs change the rightmost 0 in the output to 1; if there is no 0 in the output then prepend a 1; when 0 occurs in the input change the rightmost 1 in the output to 1; the definition of this sequence ensures that we always have a 1 in the output when a 0 occurs in the input. We this map is onto by showing the restriction to the subset Asubsequence is onto.  - Jason Kimberley, Feb 08 2013 LINKS R. K. Guy, Catwalks, sandsteps and Pascal pyramids, J. Integer Sequences, Vol. 3 (2000), Article #00.1.6. A. Karttunen, Some notes on Catalan's Triangle MAPLE # We use a simple backtracking algorithm: map(op, [seq(NonDivingLatticeSequences(j), j=1..10)]); NDLS_GLOBAL := []; NonDivingLatticeSequences := proc(n) global NDLS_GLOBAL; NDLS_GLOBAL := []; NonDivingLatticeSequencesAux(0, 0, n); RETURN(NDLS_GLOBAL); end; NonDivingLatticeSequencesAux := proc(x, h, i) global NDLS_GLOBAL; if(0 = i) then NDLS_GLOBAL := [op(NDLS_GLOBAL), x]; else if(h > 0) then NonDivingLatticeSequencesAux((2*x), h-1, i-1); fi; NonDivingLatticeSequencesAux((2*x)+1, h+1, i-1); fi; end; CROSSREFS Cf. A001405, A031443, A036990, A036991, A061855, A014486. Sequence in context: A225354 A166111 A004762 * A214432 A110086 A107746 Adjacent sequences:  A061851 A061852 A061853 * A061855 A061856 A061857 KEYWORD nonn,base,easy AUTHOR Antti Karttunen, May 11 2001 STATUS approved

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Last modified October 22 23:18 EDT 2018. Contains 316518 sequences. (Running on oeis4.)