OFFSET
1,1
EXAMPLE
sigma(33) + 33 = 81 = 3^4.
PROG
(PARI) isok(n) = ispower(sigma(n) + n, 4); \\ Michel Marcus, Jan 09 2014
CROSSREFS
KEYWORD
nonn
AUTHOR
Giovanni Resta, Feb 13 2006
EXTENSIONS
a(9)-a(26) from Donovan Johnson, Feb 01 2009
STATUS
approved