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A350388 a(n) is the largest unitary divisor of n that is a square. 21
1, 1, 1, 4, 1, 1, 1, 1, 9, 1, 1, 4, 1, 1, 1, 16, 1, 9, 1, 4, 1, 1, 1, 1, 25, 1, 1, 4, 1, 1, 1, 1, 1, 1, 1, 36, 1, 1, 1, 1, 1, 1, 1, 4, 9, 1, 1, 16, 49, 25, 1, 4, 1, 1, 1, 1, 1, 1, 1, 4, 1, 1, 9, 64, 1, 1, 1, 4, 1, 1, 1, 9, 1, 1, 25, 4, 1, 1, 1, 16, 81, 1, 1, 4 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,4
COMMENTS
First differs from A056623 at n = 32.
LINKS
FORMULA
Multiplicative with a(p^e) = p^e if e is even and 1 otherwise.
a(n) = n/A350389(n).
a(n) = A071974(n)^2.
a(n) = A008833(n) if and only if n is in A335275.
A001222(a(n)) = A350386(n).
a(n) = 1 if and only if n is an exponentially odd number (A268335).
a(n) = n if and only if n is a positive square (A000290 \ {0}).
Sum_{k=1..n} a(k) ~ c * n^(3/2), where c = (1/3) * Product_{p prime} (1 + sqrt(p)/(1 + p + p^2)) = 0.59317173657411718128... [updated Oct 16 2022]
Dirichlet g.f.: zeta(2*s-2) * zeta(2*s) * Product_{p prime} (1 + 1/p^s - 1/p^(2*s) - 1/p^(3*s-2)). - Amiram Eldar, Oct 01 2023
MATHEMATICA
f[p_, e_] := If[EvenQ[e], p^e, 1]; a[1] = 1; a[n_] := Times @@ f @@@ FactorInteger[n]; Array[a, 100]
PROG
(PARI) a(n) = {my(f = factor(n)); prod(i = 1, #f~, if(f[i, 2]%2, 1, f[i, 1]^f[i, 2])); } \\ Amiram Eldar, Oct 01 2023
CROSSREFS
Sequence in context: A119350 A016528 A368884 * A056623 A038025 A079982
KEYWORD
nonn,easy,mult
AUTHOR
Amiram Eldar, Dec 28 2021
STATUS
approved

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Last modified May 19 13:04 EDT 2024. Contains 372692 sequences. (Running on oeis4.)