A300669 Positive numbers k with two consecutive ones in the binary representation of 1/k.
5, 9, 10, 11, 13, 17, 18, 19, 20, 21, 22, 23, 25, 26, 27, 29, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 49, 50, 52, 53, 54, 55, 57, 58, 59, 61, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89
Offset: 1
Examples
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)
Programs
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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)
Comments