OFFSET
1,1
COMMENTS
The list is not exhaustive since the search was restricted to sigma(p^k) such that p<1728 and all powers k such that all primes in the factorization of sigma(p^k) are also less than 1728.
LINKS
Walter A. Kehowski, Table of n, a(n) for n = 1..1536
Walter A. Kehowski, Sigma-powerful numbers
EXAMPLE
sigma(3^4)=11^2, sigma(7^3)=2^4*5^2, sigma(2^4*5^2)=31^2, sigma(2^2*653^2)=7^2*13^2*19^2.
CROSSREFS
KEYWORD
dead
AUTHOR
Walter Kehowski, Aug 09 2010
STATUS
approved