OFFSET
1,1
COMMENTS
Equivalently, these are the numbers k such that A300655(k) > 1.
Equivalently, these are the numbers k such that A300653(k, 3) = 3.
If n belongs to this sequence then 2*n belongs to this sequence.
This sequence has similarities with A004780; here 1/k has two consecutive ones in binary, there k has two consecutive ones in binary.
See A300630 for the complementary sequence.
EXAMPLE
The first terms, alongside the binary representation of 1/a(n), are:
n a(n) bin(1/a(n)) with repeating digits in parentheses
-- ---- ------------------------------------------------
1 5 0.(0011)
2 9 0.(0001110)
3 10 0.0(0011)
4 11 0.(0001011101)
5 13 0.0(00100111011)
6 17 0.(00001111)
7 18 0.0(000111)
8 19 0.(000011010111100101)
9 20 0.00(0011)
10 21 0.(000011)
PROG
(PARI) is(n) = my (f=1/max(2, n), s=Set()); while (!setsearch(s, f), if (floor(f*4)==3, return (1), s=setunion(s, Set(f)); f=frac(f*2))); return (0)
CROSSREFS
KEYWORD
nonn,base
AUTHOR
Rémy Sigrist, Mar 11 2018
STATUS
approved