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A338753
Number of integers less than n with the same period of reciprocal as n.
0
0, 1, 0, 2, 3, 1, 0, 4, 2, 5, 0, 3, 1, 2, 4, 6, 0, 5, 0, 7, 3, 1, 0, 6, 8, 4, 0, 5, 0, 7, 0, 9, 2, 1, 6, 8, 1, 1, 7, 10, 0, 8, 0, 3, 9, 1, 0, 10, 0, 11, 2, 9, 0, 2, 4, 10, 2, 1, 0, 11, 0, 1, 11, 12, 12, 5, 0, 3, 2, 13, 0, 12, 0, 3, 13, 3, 14, 15, 1, 13, 0, 1, 0, 16, 4, 1, 2, 6, 0, 14
OFFSET
1,4
FORMULA
a(n) = |{j < n : A051626(j) = A051626(n)}|.
EXAMPLE
a(14) = 2 because A051626(14) = 6 and also A051626(7) = A051626(13) = 6.
More specifically,
1/7 = 0.142857(142857)... (period 6),
1/13 = 0.076923(076923)... (period 6),
1/14 = 0.0714285(714285)... (period 6).
MATHEMATICA
Table[Length[Select[Range[n - 1], Length[RealDigits[1/#][[1, -1]]] == Length[RealDigits[1/n][[1, -1]]] &]], {n, 90}]
CROSSREFS
Cf. A051626.
Sequence in context: A352067 A368486 A178245 * A167666 A115352 A275808
KEYWORD
nonn,base
AUTHOR
Ilya Gutkovskiy, Nov 06 2020
STATUS
approved