A353625 a(n) = 1 if n is divisible by the squares of two distinct primes, otherwise 0.

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

Offset

1

Links

Antti Karttunen, Table of n, a(n) for n = 1..65537

Index entries for characteristic functions.

Index entries for sequences computed from exponents in factorization of n.

Formula

a(n) = 1 iff A056170(n) > 1, otherwise 0.

a(n) = a(A046523(n)).

a(n) <= A353626(n).

Asymptotic mean: Limit_{m->oo} (1/m) * Sum_{k=1..m} a(k) = 1 - (6/Pi^2) * (1 + A154945) = 0.05668359058... . - Amiram Eldar, Jul 24 2022

Mathematica

a[n_] := If[Count[FactorInteger[n][[;; , 2]], _?(# > 1 &)] > 1, 1, 0]; Array[a, 100] (* Amiram Eldar, Jul 24 2022 *)

Prog

(PARI)
A056170(n) = { my(f=factor(n)[, 2]); sum(i=1, #f, f[i]>1); }; \\ From A056170
A353625(n) = (A056170(n)>1);

Crossrefs

Characteristic function of A036785.

Cf. A046523, A056170, A154945, A353626.

Sequence in context: A025469 A025466 A072769 * A322438 A304572 A070204

Adjacent sequences: A353622 A353623 A353624 * A353626 A353627 A353628

Keyword

nonn

Author

Antti Karttunen, May 02 2022

Status

approved