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URL: https://oeis.org/A389465

⇱ A389465 - OEIS

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A389465
Number of natural numbers in range [n .. sigma(n)] that are coprime to n.
3
1, 1, 1, 2, 1, 2, 1, 4, 3, 3, 1, 5, 1, 4, 5, 8, 1, 7, 1, 9, 7, 6, 1, 12, 5, 7, 9, 12, 1, 11, 1, 16, 9, 9, 10, 19, 1, 10, 11, 20, 1, 15, 1, 18, 18, 12, 1, 25, 7, 18, 13, 21, 1, 22, 13, 27, 15, 15, 1, 29, 1, 16, 24, 32, 15, 23, 1, 27, 17, 26, 1, 41, 1, 19, 27, 30, 16, 28, 1, 42, 27, 21, 1, 40, 18, 22, 21, 42, 1, 39
OFFSET
1,4
FORMULA
a(n) = Sum_{k=n..sigma(n)} [1==gcd(k,n)], where [ ] is the Iverson bracket.
a(n) = A389464(n) + A325964(n).
MATHEMATICA
A389465[n_] := Sum[Boole[CoprimeQ[k, n]], {k, n, DivisorSigma[1, n]}];
Array[A389465, 100] (* Paolo Xausa, Oct 11 2025 *)
PROG
(PARI) A389465(n) = sum(k=n, sigma(n), 1==gcd(k, n));
CROSSREFS
Row lengths of A389466.
Sequence in context: A138567 A103530 A090924 * A247074 A160595 A105778
KEYWORD
nonn
AUTHOR
Antti Karttunen, Oct 10 2025
STATUS
approved