OFFSET
1,2
COMMENTS
Numbers k such that sigma(sigma(k)) = 2^e * sigma(k), for some e >= 0.
Numbers k such that sigma(k) is in A336702.
If there existed any hypothetical 3-perfect number (A005820) of the form x = 4u+2 and not divisible by 3, then x would be also included in this sequence, as then sigma(sigma(x)) = 12*x = 4*sigma(x). Such x would be also a term of A349745 and of A351458, and x/2 would be a rare odd term of A000396, and also in A336702. See also the diagram in A347392.
PROG
CROSSREFS
Subsequence of A066961.
KEYWORD
nonn
AUTHOR
Antti Karttunen, Apr 17 2022
STATUS
approved