A368625 Characteristic function of non-refactorable numbers (A159973).

0, 0, 1, 1, 1, 1, 1, 0, 0, 1, 1, 0, 1, 1, 1, 1, 1, 0, 1, 1, 1, 1, 1, 0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 1, 1, 1, 0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 1, 1, 1, 0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 1, 1, 1, 1, 1, 1, 1, 0, 1, 1, 1, 0, 1, 1, 1, 0, 1, 1, 1, 1, 1, 1, 1, 0, 1

Offset

1,1

Links

Table of n, a(n) for n=1..97.

Eric Weisstein's World of Mathematics, Refactorable Number

Index entries for characteristic functions

Formula

a(n) = ceiling(n/d(n))-floor(n/d(n)), where d(n) is the number of divisors of n (A000005).

a(n) = 1 - A336040(n).

Mathematica

Table[(Ceiling[n/DivisorSigma[0, n]] - Floor[n/DivisorSigma[0, n]]), {n, 100}]

Crossrefs

Cf. A000005, A033950 (refactorable numbers), A159973, A336040.

Sequence in context: A131735 A131736 A152228 * A086823 A228487 A295306

Adjacent sequences: A368622 A368623 A368624 * A368626 A368627 A368628

Keyword

nonn,easy

Author

Wesley Ivan Hurt, Jan 01 2024

Status

approved