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A359466
a(n) = 1 if n has exactly one non-unitary prime factor, otherwise 0.
7
0, 0, 0, 1, 0, 0, 0, 1, 1, 0, 0, 1, 0, 0, 0, 1, 0, 1, 0, 1, 0, 0, 0, 1, 1, 0, 1, 1, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 1, 1, 0, 0, 1, 1, 1, 0, 1, 0, 1, 0, 1, 0, 0, 0, 1, 0, 0, 1, 1, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 1, 1, 0, 0, 0, 1, 1, 0, 0, 1, 0, 0, 0, 1, 0, 1, 0, 1, 0, 0, 0, 1, 0, 1, 1, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 1, 1, 0, 0, 1, 1, 0, 0, 1, 1
OFFSET
1
FORMULA
a(n) = [A056170(n) == 1], where [ ] is the Iverson bracket.
a(n) = A353670(A181819(n)).
a(n) >= A359472(n) and a(n) >= A359474(n).
Sum_{k=1..n} a(k) ~ c * n, where c = A059956 * A154945 = 0.335389... . - Amiram Eldar, Jan 05 2023
MATHEMATICA
a[n_] := If[Count[(f = FactorInteger[n])[[;; , 2]], 1] == Length[f] - 1, 1, 0]; Array[a, 100] (* Amiram Eldar, Jan 05 2023 *)
PROG
(PARI) A359466(n) = { my(f=factor(n)); (1==#select(x->(x>1), f[, 2])); }; \\ After isok function in A190641
CROSSREFS
Characteristic function of A190641.
Differs from A359467 for the first time at n=225, where a(225) = 0, while A359467(225) = 1.
Sequence in context: A319710 A345951 A345952 * A359467 A359469 A107078
KEYWORD
nonn
AUTHOR
Antti Karttunen, Jan 02 2023
STATUS
approved