OFFSET
1,1
COMMENTS
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000
EXAMPLE
The fourth Zumkeller number is 24, since sigma(24) = A000203(24) = 60, 60/2 = 30, and the divisors of 24 can be partitioned as 1 + 2 + 3 + 4 + 8 + 12 = 6 + 24 = 30.
In turn, 30 is also a Zumkeller number, as sigma(30)/2 = 72/2 = 36 and 1 + 2 + 3 + 5 + 10 + 15 = 6 + 30 = 36.
Therefore 24 is in this sequence.
But since 36 is not a Zumkeller number at all, 30 is not in this sequence.
MATHEMATICA
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Ivan N. Ianakiev, Oct 09 2017
STATUS
approved