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 A285099 a(n) is the zero-based index of the second least significant 1-bit in the base-2 representation of n, or 0 if there are fewer than two 1-bits in n. 5
 0, 0, 0, 1, 0, 2, 2, 1, 0, 3, 3, 1, 3, 2, 2, 1, 0, 4, 4, 1, 4, 2, 2, 1, 4, 3, 3, 1, 3, 2, 2, 1, 0, 5, 5, 1, 5, 2, 2, 1, 5, 3, 3, 1, 3, 2, 2, 1, 5, 4, 4, 1, 4, 2, 2, 1, 4, 3, 3, 1, 3, 2, 2, 1, 0, 6, 6, 1, 6, 2, 2, 1, 6, 3, 3, 1, 3, 2, 2, 1, 6, 4, 4, 1, 4, 2, 2, 1, 4, 3, 3, 1, 3, 2, 2, 1, 6, 5, 5, 1, 5, 2, 2, 1, 5, 3, 3, 1, 3, 2, 2, 1, 5, 4, 4, 1, 4, 2, 2, 1, 4 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,6 LINKS Antti Karttunen, Table of n, a(n) for n = 0..8192 Index entries for sequences related to binary expansion of n FORMULA If A000120(n) < 2, a(n) = 0, otherwise a(n) = A007814(A129760(n)) = A007814(n AND (n-1)). [Where AND is bitwise-and, A004198]. From Jeffrey Shallit, Apr 19 2020: (Start) This is a 2-regular sequence, satisfying the identities a(4n) = -a(n) + a(2n), a(4n+2) = a(4n+1), a(8n+1) = -a(2n+1) + 2a(4n+1), a(8n+3) = a(4n+3), a(8n+5) = 2a(4n+3), a(8n+7) = a(4n+3). (End) EXAMPLE For n = 3, "11" in binary, the second least significant 1-bit (the second 1-bit from the right) is at position 1 (when the rightmost position is position 0), thus a(3) = 1. For n = 4, "100" in binary, there is just one 1-bit present, thus a(4) = 0. For n = 5, "101" in binary, the second 1-bit from the right is at position 2, thus a(5) = 2. For n = 25, "11001" in binary, the second 1-bit from the right is at position 3, thus a(25) = 3. MATHEMATICA a007814[n_]:=IntegerExponent[n, 2]; a[n_]:=If[DigitCount[n, 2, 1]<2, 0, a007814[BitAnd[n, n - 1]]]; Table[a[n], {n, 0, 150}] (* Indranil Ghosh, Apr 20 2017 *) PROG (Scheme) (define (A285099 n) (if (<= (A000120 n) 1) 0 (A007814 (A004198bi n (- n 1))))) ;; A004198bi implements bitwise-and. (Python) import math def a007814(n): return int(math.log(n - (n & n - 1), 2)) def a(n): return 0 if bin(n)[2:].count("1") < 2 else a007814(n & (n - 1)) # Indranil Ghosh, Apr 20 2017 CROSSREFS Cf. A000120, A004198, A007814, A129760, A285097. Sequence in context: A258291 A146527 A352556 * A306754 A063250 A348967 Adjacent sequences: A285096 A285097 A285098 * A285100 A285101 A285102 KEYWORD nonn,base AUTHOR Antti Karttunen, Apr 19 2017 STATUS approved

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Last modified June 9 15:05 EDT 2023. Contains 363181 sequences. (Running on oeis4.)