A325123 - OEIS

A325123

Number of divisible pairs of positive integers up to n with no binary carries.

0, 0, 1, 1, 3, 3, 4, 4, 7, 7, 9, 9, 12, 12, 13, 13, 17, 17, 19, 19, 22, 22, 23, 23, 28, 28, 29, 29, 31, 31, 32, 32, 37, 37, 39, 39, 44, 44, 45, 45, 50, 50, 52, 52, 54, 54, 55, 55, 62, 62, 64, 64, 66, 66, 68, 68, 72, 72, 73, 73, 76, 76, 77, 77, 83, 83, 85, 85

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OFFSET

0,5

COMMENTS

Two positive integers are divisible if the first divides the second, and they have a binary carry if the positions of 1's in their reversed binary expansion overlap.

a(2k+1) = a(2k), since an odd number and any divisor will overlap in the last digit. Additionally, a(2k+2) > a(2k+1) because the pair {1,2k+2} is always valid. Therefore, every term appears exactly twice. - Charlie Neder, Apr 02 2019

LINKS

Table of n, a(n) for n=0..67.

EXAMPLE

The a(2) = 1 through a(11) = 9 pairs:

{1,2} {1,2} {1,2} {1,2} {1,2} {1,2} {1,2} {1,2} {1,2} {1,2}

{1,4} {1,4} {1,4} {1,4} {1,4} {1,4} {1,4} {1,4}

{2,4} {2,4} {1,6} {1,6} {1,6} {1,6} {1,6} {1,6}

{2,4} {2,4} {1,8} {1,8} {1,8} {1,8}

{2,4} {2,4} {2,4} {2,4}

{2,8} {2,8} {2,8} {2,8}

{4,8} {4,8} {4,8} {4,8}

{1,10} {1,10}

{5,10} {5,10}

MATHEMATICA

Table[Length[Select[Tuples[Range[n], 2], Divisible@@Reverse[#]&&Intersection[Position[Reverse[IntegerDigits[#[[1]], 2]], 1], Position[Reverse[IntegerDigits[#[[2]], 2]], 1]]=={}&]], {n, 0, 20}]

CROSSREFS

Cf. A006218, A019565, A050315, A070939, A080572, A247935, A267610.

Cf. A325095, A325096, A325101, A325103, A325104, A325105, A325106, A325124.

Sequence in context: A007768 A180018 A011371 * A097355 A258057 A003860

Adjacent sequences: A325120 A325121 A325122 * A325124 A325125 A325126

KEYWORD

nonn

AUTHOR

Gus Wiseman, Mar 29 2019

STATUS

approved