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A361465 a(n) = 1 if A017665(n) [the numerator of the sum of the reciprocals of the divisors of n] is a power of 2, otherwise 0. 4
1, 0, 1, 0, 0, 1, 1, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 1, 0, 0, 1, 0, 1, 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, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 1, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1 (list; graph; refs; listen; history; text; internal format)
OFFSET
1
LINKS
FORMULA
a(n) = A209229(A017665(n)).
If a(x) = a(y) = gcd(x, y) = 1, then also a(x*y) = 1.
MATHEMATICA
pow[n_] := If[n == 2^IntegerExponent[n, 2], 1, 0];
a[n_] := pow[Numerator[DivisorSigma[-1, n]]]; Array[a, 100] (* Amiram Eldar, Mar 20 2023 *)
PROG
(PARI)
A017665(n) = numerator(sigma(n)/n);
A209229(n) = (n && !bitand(n, n-1));
CROSSREFS
Characteristic function of A043305.
Cf. A017665, A209229, A355943 [= A000035(n)*a(n)], A361466 [= a(A003961(n))].
Sequence in context: A188467 A039983 A152490 * A145273 A295892 A120522
KEYWORD
nonn
AUTHOR
Antti Karttunen, Mar 20 2023
STATUS
approved

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Last modified April 14 20:39 EDT 2024. Contains 371667 sequences. (Running on oeis4.)