OFFSET
1,1
COMMENTS
No other terms less than 10^8. The corresponding composite numbers are 6, 40, 136, and 3352. Is this sequence finite? See A158913 for the sequence for sigma_1.
MATHEMATICA
tp=DivisorSigma[2, Select[Range[4000], PrimeQ]]; tc=DivisorSigma[2, Select[Range[4000], !PrimeQ[ # ]&]]; Sqrt[Intersection[tp, tc]-1]
CROSSREFS
KEYWORD
more,nonn
AUTHOR
T. D. Noe, Mar 30 2009
STATUS
approved