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%I #13 Feb 18 2024 09:06:33
%S 1,110,798,8904
%N Numbers k such that k-th prime = sigma(sigma(k)) + 1.
%C There are no other numbers < 3400000. - _Stefan Steinerberger_, Nov 20 2005
%e sigma(sigma(110)) + 1 = sigma(216) + 1 = 601 = prime(110).
%t Select[Range[10^6], Prime[ # ] == DivisorSigma[1, DivisorSigma[1, # ]] + 1 &]
%o (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)
%K nonn,more
%O 1,2
%A _Joseph L. Pe_, Sep 18 2002