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Search: id:A161819
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| A161819 |
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a(n) = the smallest integer > n such that both n and a(n), when represented in binary, contain the same types of runs of 1's, the runs being in any order. |
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+0
5
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| 2, 4, 6, 8, 9, 12, 14, 16, 10, 17, 13, 24, 19, 28, 30, 32, 18, 20, 22, 33, 37, 25, 29, 48, 26, 35, 51, 56, 39, 60, 62, 64, 34, 36, 38, 40, 41, 44, 46, 65, 42, 69, 45, 49, 53, 57, 61, 96, 50, 52, 54, 67, 75, 99, 59, 112, 58, 71, 103, 120, 79, 124, 126, 128, 66, 68, 70, 72, 73
(list; graph; listen)
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OFFSET
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1,1
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COMMENT
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Clarification of definition: Think of binary n and a(n) each as a string of 0's and 1's. Consider the "runs" of 1's in binary n and a(n), where each run is made up completely of 1's, and is bounded on both sides either by 0's or by the edge of the string. Now consider the lengths of each bounded run of 1's (the number of 1's in each run). Then a(n) is the smallest integer greater than n whose set of run-lengths is a permutation of the set of run-lengths for n. (See example.)
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EXAMPLE
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77 in binary is 1001101. There are three runs of 1's, two runs of one 1 each and one run of two 1's. So we are looking for the smallest integer > 77 with two runs of one 1 each and one run of two 1's (and no other runs of 1's). For example, 78 in binary is 1001110, which contains the runs, except that it is required that each run be bounded by 0's or the edge of the binary string. The next number that fits the requirements completely is 83 = 1010011 in binary. So a(77) = 83.
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MAPLE
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rtype := proc(n) local rt, bdgs, pr, i, rl ; rt := [seq(0, i=1..40)] ; bdgs := convert(n, base, 2) ; pr := 0 ; for i from 1 to nops(bdgs) do if op(i, bdgs) = 1 then if pr = 0 then rl := 0 ; fi; rl := rl+1 ; else if pr = 1 then rt := subsop(rl=op(rl, rt)+1, rt) ; fi; fi; pr := op(i, bdgs) ; if i = nops(bdgs) and pr = 1 then rt := subsop(rl=op(rl, rt)+1, rt) ; fi; od: rt ; end: A161819 := proc(n) local rtn, a; rtn := rtype(n) ; for a from n+1 do if rtype(a) = rtn then RETURN(a) ; fi; od: end: seq(A161819(n), n=1..100) ; [From R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Jul 20 2009]
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CROSSREFS
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A161820, A161821, A161822
Sequence in context: A047294 A143346 A138969 this_sequence A071562 A100345 A118363
Adjacent sequences: A161816 A161817 A161818 this_sequence A161820 A161821 A161822
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KEYWORD
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base,nonn
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AUTHOR
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Leroy Quet (q1qq2qqq3qqqq(AT)yahoo.com), Jun 20 2009
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EXTENSIONS
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More terms from R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Jul 20 2009
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