A363298 Number of refactorable unitary divisors of n.

1, 2, 1, 1, 1, 2, 1, 2, 2, 2, 1, 2, 1, 2, 1, 1, 1, 4, 1, 1, 1, 2, 1, 3, 1, 2, 1, 1, 1, 2, 1, 1, 1, 2, 1, 3, 1, 2, 1, 3, 1, 2, 1, 1, 2, 2, 1, 1, 1, 2, 1, 1, 1, 2, 1, 3, 1, 2, 1, 3, 1, 2, 2, 1, 1, 2, 1, 1, 1, 2, 1, 4, 1, 2, 1, 1, 1, 2, 1, 2, 1, 2, 1, 3, 1, 2, 1, 3, 1, 4

Offset

1,2

Links

Table of n, a(n) for n=1..90.

Formula

a(n) = Sum_{d|n, tau(d)|d, gcd(d,n/d)=1} 1.

Mathematica

a[n_] := DivisorSum[n, 1 &, CoprimeQ[#, n/#] && Divisible[#, DivisorSigma[0, #]] &]; Array[a, 100] (* Amiram Eldar, May 26 2023 *)

Crossrefs

Cf. A034444, A336041, A363085.

Sequence in context: A290257 A196942 A184304 * A025909 A025899 A025869

Adjacent sequences: A363295 A363296 A363297 * A363299 A363300 A363301

Keyword

nonn,easy

Author

Wesley Ivan Hurt, May 26 2023

Status

approved