A347879 The nearest common ancestor of n and sigma(n) in the Doudna tree (A005940).

1, 2, 2, 2, 3, 6, 2, 2, 2, 2, 3, 3, 7, 3, 6, 2, 2, 2, 5, 10, 2, 2, 3, 6, 2, 5, 2, 28, 3, 2, 2, 2, 3, 2, 6, 2, 19, 3, 7, 3, 5, 3, 11, 5, 3, 2, 3, 3, 2, 2, 2, 2, 2, 2, 2, 3, 5, 3, 3, 3, 31, 3, 5, 2, 5, 2, 17, 5, 3, 2, 2, 2, 37, 17, 2, 3, 6, 5, 5, 5, 4, 5, 5, 5, 2, 7, 3, 3, 3, 3, 5, 5, 2, 2, 3, 3, 2, 2, 7, 2, 13, 2

Offset: 1

Author

Antti Karttunen, Oct 13 2021

Keywords

• nonn

Comments

The fixed points of this sequence is given by the union of {2} and A336702.

The positions x such that a(x) = A252463(x) is given by the union of {1} and A347391.

The positions x such that a(x) = A252463(A252463(x)) is given by the union of {1} and A347392.

Links

• Antti Karttunen, Table of n, a(n) for n = 1..20000
• Index entries for sequences computed from indices in prime factorization
• Index entries for sequences related to sigma(n)

Crossrefs

Cf. A000203, A005940, A252463, A332221, A336702, A347381, A347391, A347392, A348040, A348041.

Programs

PARI

A347879(n) = A348041sq(n,sigma(n)); \\ Needs also code from A348041.

Formula

a(n) = A348041(n, A000203(n)).