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A325104
Number of increasing pairs of positive integers up to n with at least one binary carry.
16
0, 0, 0, 2, 2, 5, 9, 15, 15, 20, 26, 35, 43, 54, 66, 80, 80, 89, 99, 114, 126, 143, 161, 182, 198, 219, 241, 266, 290, 317, 345, 375, 375, 392, 410, 437, 457, 486, 516, 551, 575, 608, 642, 681, 717, 758, 800, 845, 877, 918, 960, 1007, 1051, 1100, 1150, 1203
OFFSET
0,4
COMMENTS
A binary carry of two positive integers is an overlap of the positions of 1's in their reversed binary expansion.
The version for ordered pairs is A080572.
FORMULA
a(n) = 2 * A080572(n - 2) + n.
EXAMPLE
The a(3) = 2 through a(8) = 15 pairs:
{1,3} {1,3} {1,3} {1,3} {1,3} {1,3}
{2,3} {2,3} {1,5} {1,5} {1,5} {1,5}
{2,3} {2,3} {1,7} {1,7}
{3,5} {2,6} {2,3} {2,3}
{4,5} {3,5} {2,6} {2,6}
{3,6} {2,7} {2,7}
{4,5} {3,5} {3,5}
{4,6} {3,6} {3,6}
{5,6} {3,7} {3,7}
{4,5} {4,5}
{4,6} {4,6}
{4,7} {4,7}
{5,6} {5,6}
{5,7} {5,7}
{6,7} {6,7}
MATHEMATICA
Table[Length[Select[Subsets[Range[n], {2}], Intersection[Position[Reverse[IntegerDigits[#[[1]], 2]], 1], Position[Reverse[IntegerDigits[#[[2]], 2]], 1]]!={}&]], {n, 0, 30}]
KEYWORD
nonn
AUTHOR
Gus Wiseman, Mar 28 2019
STATUS
approved