A347879 - OEIS

%I #13 Jan 30 2022 09:51:12

%S 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,

%T 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,

%U 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

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

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

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

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

%H Antti Karttunen, <a href="/A347879/b347879.txt">Table of n, a(n) for n = 1..20000</a>

%H <a href="/index/Pri#prime_indices">Index entries for sequences computed from indices in prime factorization</a>

%H <a href="/index/Si#SIGMAN">Index entries for sequences related to sigma(n)</a>

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

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

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

%K nonn

%O 1,2

%A _Antti Karttunen_, Oct 13 2021