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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
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 OFFSET 1 LINKS Antti Karttunen, Table of n, a(n) for n = 1..100000 Index entries for characteristic functions Index entries for sequences related to sigma(n) 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)); A361465(n) = A209229(A017665(n)); 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 Adjacent sequences: A361462 A361463 A361464 * A361466 A361467 A361468 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.)