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 A074240 Numbers n such that n-th prime = sigma(sigma(n)) + 1. 0
 1, 110, 798, 8904 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS There are no other numbers < 3400000. - Stefan Steinerberger, Nov 20 2005 LINKS Table of n, a(n) for n=1..4. 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 Sequence in context: A250529 A251037 A251038 * A283084 A283180 A283284 Adjacent sequences: A074237 A074238 A074239 * A074241 A074242 A074243 KEYWORD nonn AUTHOR Joseph L. Pe, Sep 18 2002 STATUS approved

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Last modified December 8 23:09 EST 2023. Contains 367680 sequences. (Running on oeis4.)