OFFSET
1,1
EXAMPLE
96 = sigma(42) = sigma(62) = sigma(69) = sigma(77).
MATHEMATICA
a = Table[ 0, {5000} ]; Do[ s = DivisorSigma[ 1, n ]; If[ s < 5001, a[ [ s ] ]++ ], {n, 1, 5000} ]; Select[ Range[ 5000 ], a[ [ # ] ] == 4 & ]
CROSSREFS
KEYWORD
nonn
AUTHOR
Robert G. Wilson v, Apr 18 2001
STATUS
approved