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A372381
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The number of divisors of the largest divisor of n whose number of divisors is a power of 2.
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2
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1, 2, 2, 2, 2, 4, 2, 4, 2, 4, 2, 4, 2, 4, 4, 4, 2, 4, 2, 4, 4, 4, 2, 8, 2, 4, 4, 4, 2, 8, 2, 4, 4, 4, 4, 4, 2, 4, 4, 8, 2, 8, 2, 4, 4, 4, 2, 8, 2, 4, 4, 4, 2, 8, 4, 8, 4, 4, 2, 8, 2, 4, 4, 4, 4, 8, 2, 4, 4, 8, 2, 8, 2, 4, 4, 4, 4, 8, 2, 8, 4, 4, 2, 8, 4, 4, 4
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OFFSET
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1,2
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COMMENTS
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Also, the number of infinitary divisors of the largest divisor of n whose number of divisors is a power of 2.
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LINKS
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FORMULA
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Multiplicative with a(p^e) = 2^floor(log_2(e+1)).
a(n) <= A372380(n), with equality if and only if n is cubefree (A004709).
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MATHEMATICA
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f[p_, e_] := 2^Floor[Log2[e + 1]]; a[1] = 1; a[n_] := Times @@ f @@@ FactorInteger[n]; Array[a, 100]
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PROG
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(PARI) a(n) = vecprod(apply(x -> 2^exponent(x+1), factor(n)[, 2]));
(Python)
from math import prod
from sympy import factorint
def A372381(n): return prod(1<<(e+1).bit_length()-1 for e in factorint(n).values()) # Chai Wah Wu, Apr 30 2024
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CROSSREFS
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KEYWORD
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nonn,easy,mult
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AUTHOR
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STATUS
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approved
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