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 A090569 The survivor w(n,2) in a modified Josephus problem, with a step of 2. 5
 1, 1, 3, 3, 1, 1, 3, 3, 9, 9, 11, 11, 9, 9, 11, 11, 1, 1, 3, 3, 1, 1, 3, 3, 9, 9, 11, 11, 9, 9, 11, 11, 33, 33, 35, 35, 33, 33, 35, 35, 41, 41, 43, 43, 41, 41, 43, 43, 33, 33, 35, 35, 33, 33, 35, 35, 41, 41, 43, 43, 41, 41, 43, 43, 1, 1, 3, 3, 1, 1, 3, 3, 9, 9, 11, 11, 9, 9, 11, 11, 1, 1 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 COMMENTS Arrange n persons {1,2,...,n} consecutively on a line rather than around in a circle. Beginning at the left end of the line, we remove every q-th person until we reach the end of the line. At this point we immediately reverse directions, taking care not to "double count" the person at the end of the line and continue to eliminate every q-th person, but now moving right to left. We continue removing people in this back-and-forth manner until there remains a lone survivor w(n,q). Or a(n) is in A145812 such that 2n+1-2a(n) is in A145812 as well. Note also that 2a(n)+A088442(n-1)=2n+1. - Vladimir Shevelev, Oct 20 2008 LINKS Chris GroĆ«r, The Mathematics of Survival: From Antiquity to the Playground, Amer. Math. Monthly, 110 (No. 9, 2003), 812-825. FORMULA w(n, 2) = 1 + Sum_{odd j=1..k} b(j)*(2^j), where Sum_{j=0..k} b(j)*(2^j) is the binary expansion of either n or n-1, whichever is odd. a(n) = A063695(n-1) + 1. EXAMPLE a(2)=11, since people are eliminated in the order 2, 4, 6, 8, 10, 12, 9, 5, 1, 7, 3, leaving 11 as the survivor. CROSSREFS Cf. A088443, A088452. Sequence in context: A266529 A266509 A266539 * A160324 A197928 A109439 Adjacent sequences:  A090566 A090567 A090568 * A090570 A090571 A090572 KEYWORD nonn AUTHOR John W. Layman, Dec 02 2003 STATUS approved

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Last modified May 7 16:00 EDT 2021. Contains 343652 sequences. (Running on oeis4.)