cp's OEIS Frontend

This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.

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A187788 a(n) is the least step for the Sankt-Petrus-game with n white and n black stones.

Original entry on oeis.org

2, 5, 2, 4, 3, 11, 2, 3, 8, 16, 4, 21, 6, 5, 2, 11, 20, 34, 8, 15, 10, 7, 13, 11, 13, 45, 18, 23, 8, 3, 2, 25, 75, 42, 13, 5, 23, 13, 50, 16, 18, 89, 38, 8, 39, 30, 29, 38, 7, 45, 23, 137, 46, 63, 17, 48, 5, 46, 34, 140, 33, 39, 2, 28, 29, 79, 33, 48, 3, 10, 46, 120, 6, 37, 17, 8, 44, 15, 160, 20, 35, 144, 104, 179, 153, 24, 8, 265, 19, 9, 62, 7, 139, 19, 44, 93, 182, 27, 158, 185
Offset: 1

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Author

Paul Weisenhorn, Jan 06 2013

Keywords

Comments

Beginning at the position A187789(n) with step a(n), (n-1) white stones were eliminated; then from the position 1 of the last white stone, n black stones were eliminated.

Examples

			n=4; WBWWBBWB; startposition=A187789(4)=8; least step=a(4)=4; elimination: white stones: {3,7,4}; black stones: {6,5,8,2}.
		

References

  • W. Ahrens, Das Josephusspiel, Archiv für Kulturgeschichte, Jg 11(1913), 129-151.

Crossrefs

First column in A321781.

Programs

  • Maple
    s:=1: M:={}:
    for n from 1 to 100 do M:=M union {n}:
    while (M <> {}) do
      s1:=s: s:=s+1: f[1]:=1:
      for n from 2 to 101 do  n1:=n-1:
        f[n]:=(f[n1]+s1) mod n +1:
        if (f[n]=1) and (n1 in M) then
          a[n1]:=s: M:=M minus {n1}:
        end if:
      end do:
    end do:
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