login

Reminder: The OEIS is hiring a new managing editor, and the application deadline is January 26.

Numbers k for which A335915(sigma(k)) = A335915(sigma(sigma(k))).
5

%I #5 Jul 24 2020 10:58:32

%S 1,2,5,12,19,24,27,28,38,39,44,54,56,59,60,65,78,83,84,87,92,95,123,

%T 124,129,133,136,143,160,167,168,178,212,223,248,258,259,266,269,276,

%U 285,288,297,308,360,393,395,413,427,429,437,446,455,473,479,501,518,522,528,555,560,581,611,612,681,738,752,755

%N Numbers k for which A335915(sigma(k)) = A335915(sigma(sigma(k))).

%C Numbers k for which A336455(k) = A336455(sigma(k)) = A336456(k).

%C Numbers k such that sigma(k) is in A336461.

%C See comments in A336464.

%H <a href="/index/O#opnseqs">Index entries for sequences where odd perfect numbers must occur, if they exist at all</a>

%o (PARI)

%o A000265(n) = (n>>valuation(n,2));

%o A335915(n) = { my(f=factor(n)); prod(k=1,#f~,if(2==f[k,1],1,(A000265((f[k,1]^2)-1)^f[k,2]))); };

%o isA336462(n) = (A335915(sigma(n))==A335915(sigma(sigma(n))));

%Y Cf. A000203, A000265, A335915, A336455, A336456.

%Y Cf. also A336461, A336463, A336464.

%K nonn

%O 1,2

%A _Antti Karttunen_, Jul 22 2020