OFFSET
1,2
EXAMPLE
16447*sigma(16447)*sigma(sigma(16447)) = T(4210431).
PROG
(PARI) isok(n) = ispolygonal(n*sigma(n)*sigma(sigma(n)), 3); \\ Michel Marcus, Jan 27 2014
CROSSREFS
KEYWORD
nonn
AUTHOR
Giovanni Resta, Feb 13 2006
EXTENSIONS
a(5) from Donovan Johnson, Mar 09 2014
STATUS
approved