OFFSET
1,1
LINKS
Donovan Johnson, Table of n, a(n) for n = 1..1000
Mersenne Forum, Perfect roots
EXAMPLE
n = 22446139 = 31*67*101*107. sopfr(n) = 31+67+101+107 = 306, d(n) = 2^4 = 16, sigma(n) = (31+1)*(67+1)*(101+1)*(107+1) = 23970816, (sopfr(n)*d(n))^2 = (306*16)^2 = 23970816 = sigma(n).
CROSSREFS
KEYWORD
nonn
AUTHOR
Fred Schneider, Dec 14 2006
EXTENSIONS
Clarified and extended by Charles R Greathouse IV, Oct 11 2009
Clarified by Donovan Johnson, Jun 09 2013
STATUS
approved