A379769 a(n) = (A006218(n) mod n).

0, 1, 2, 0, 0, 2, 2, 4, 5, 7, 7, 11, 11, 13, 0, 2, 1, 4, 3, 6, 7, 8, 7, 12, 12, 13, 14, 17, 16, 21, 20, 23, 24, 25, 26, 32, 31, 32, 33, 38, 37, 0, 41, 0, 2, 2, 0, 6, 5, 7, 7, 9, 7, 11, 11, 15, 15, 15, 13, 21, 19, 19, 21, 24, 24, 28, 26, 28, 28, 32, 30, 38, 36, 36, 38, 40, 40, 44

Offset

1,3

Links

Michel Marcus, Table of n, a(n) for n = 1..10000

Formula

a(A050226(k)) = 0.

Example

n = 7: a(7) = A006218(7) mod 7 = 2.

Mathematica

With[{nmax = 100}, Mod[Accumulate[DivisorSigma[0, Range[nmax]]], Range[nmax]]] (* Amiram Eldar, Jan 06 2025 *)

Prog

(PARI) a(n) = sum(k=1, n, numdiv(k)) % n; \\ Michel Marcus, Jan 06 2025
(Python)
from math import isqrt
def A379769(n):
    s = isqrt(n)
    c = -pow(s, 2, n)
    for k in range(1, s+1):
        c = (c+(n//k<<1))%n
    return c # Chai Wah Wu, Jan 30 2026

Crossrefs

Cf. A006218, A050226.

Sequence in context: A033718 A033737 A033747 * A087611 A282133 A338819

Adjacent sequences: A379766 A379767 A379768 * A379770 A379771 A379772

Keyword

nonn,look

Author

Ctibor O. Zizka, Jan 06 2025

Status

approved