A074240 Numbers n such that n-th prime = sigma(sigma(n)) + 1.

1, 110, 798, 8904

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