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A180090
Sigma-powerful numbers: powerful numbers n such that sigma(n) is also powerful. An incomplete version of A337045.
7
81, 343, 400, 1705636, 3648100, 13645088, 25992000, 26680500, 29184800, 80802000, 110215125, 178054848, 180093375, 213444000, 310144500, 408632609, 575664500, 1055340196, 1120504500, 1476326929, 1667329664, 2066544500
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, 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