A338569 Number of integers less than n with the same number of ordered factorizations as n.

0, 1, 2, 0, 3, 0, 4, 0, 1, 1, 5, 0, 6, 2, 3, 1, 7, 2, 8, 3, 4, 5, 9, 0, 2, 6, 1, 4, 10, 0, 11, 0, 7, 8, 9, 0, 12, 10, 11, 1, 13, 1, 14, 5, 6, 12, 15, 0, 3, 7, 13, 8, 16, 2, 14, 3, 15, 16, 17, 0, 18, 17, 9, 0, 18, 2, 19, 10, 19, 3, 20, 0, 21, 20, 11, 12, 21, 4, 22, 1

Offset

1,3

Links

Table of n, a(n) for n=1..80.

Eric Weisstein's World of Mathematics, Ordered Factorization

Formula

a(n) = |{j < n : A074206(j) = A074206(n)}|.

Example

a(14) = 2 because A074206(14) = 3 and also A074206(6) = A074206(10) = 3.

Mathematica

A074206[1] = 1; A074206[n_] := A074206[n] = A074206 /@ Most[Divisors[n]] // Total; Table[Length[Select[Range[n - 1], A074206[#] == A074206[n] &]], {n, 80}]

Crossrefs

Cf. A047983, A074206, A338568.

Sequence in context: A352740 A108416 A215395 * A343757 A108760 A343554

Adjacent sequences: A338566 A338567 A338568 * A338570 A338571 A338572

Keyword

nonn

Author

Ilya Gutkovskiy, Nov 02 2020

Status

approved