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A353625
a(n) = 1 if n is divisible by the squares of two distinct primes, otherwise 0.
2
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
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.
Sequence in context: A025469 A025466 A072769 * A322438 A304572 A070204
KEYWORD
nonn
AUTHOR
Antti Karttunen, May 02 2022
STATUS
approved