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.

A300655 a(n) is the length of the longest contiguous block of ones in the binary expansion of 1/n.

Original entry on oeis.org

1, 1, 1, 1, 2, 1, 1, 1, 3, 2, 3, 1, 3, 1, 1, 1, 4, 3, 4, 2, 2, 3, 2, 1, 4, 3, 4, 1, 4, 1, 1, 1, 5, 4, 3, 3, 5, 4, 2, 2, 5, 2, 5, 3, 2, 2, 3, 1, 4, 4, 1, 3, 5, 4, 4, 1, 5, 4, 5, 1, 5, 1, 1, 1, 6, 5, 6, 4, 3, 3, 3, 3, 3, 5, 3, 4, 4, 2, 4, 2, 6, 5, 6, 2, 2, 5, 4
Offset: 1

Views

Author

Rémy Sigrist, Mar 10 2018

Keywords

Comments

This sequence has similarities with A038374: here we consider the binary expansion of 1/n, there the binary expansion of n.

Examples

			The first terms, alongside the binary representation of 1/n, are:
  n   a(n)  bin(1/n) with repeating digits in parentheses
  --  ----  ---------------------------------------------
   1     1  1.(0)
   2     1  0.1(0)
   3     1  0.(01)
   4     1  0.01(0)
   5     2  0.(0011)
   6     1  0.0(01)
   7     1  0.(001)
   8     1  0.001(0)
   9     3  0.(000111)
  10     2  0.0(0011)
  11     3  0.(0001011101)
  12     1  0.00(01)
  13     3  0.(000100111011)
  14     1  0.0(001)
  15     1  0.(0001)
  16     1  0.0001(0)
  17     4  0.(00001111)
  18     3  0.0(000111)
  19     4  0.(000011010111100101)
  20     2  0.00(0011)
		

Crossrefs

Programs

  • PARI
    a(n) = my (w=1, s=Set(), f=1/max(n,2)); while (!setsearch(s,f), while (floor(f*2^(w+1))==2^(w+1)-1, w++); s=setunion(s,Set(f)); f=frac(f*2)); return (w)

Formula

a(2*n) = a(n).
a(2^k + 1) = k for any k > 0.
a(n) = 1 iff n belongs to A300630.