OFFSET
1,2
COMMENTS
There are no other numbers < 3400000. - Stefan Steinerberger, Nov 20 2005
EXAMPLE
sigma(sigma(110)) + 1 = sigma(216) + 1 = 601 = prime(110).
MATHEMATICA
Select[Range[10^6], Prime[ # ] == DivisorSigma[1, DivisorSigma[1, # ]] + 1 &]
PROG
(MuPAD) ind := 1; nu := 2; repeat w := numlib::sigma(numlib::sigma(ind))+1; if w = nu then print(ind); end_if; ind := ind+1; nu := nextprime(nu+1); until ind>3400000 end_repeat; (Steinerberger)
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Joseph L. Pe, Sep 18 2002
STATUS
approved