A050781 - OEIS

A050781

Numbers k such that sopfr(k) = sopfr(k - sopfr(k)).

55, 72, 84, 119, 143, 256, 2106, 2211, 2279, 3024, 3150, 3551, 4284, 6360, 6500, 9350, 10200, 10285, 10919, 13560, 14279, 14351, 15606, 16463, 17063, 23595, 25011, 27208, 28208, 28600, 31460, 33096, 42180, 44330, 52320, 53053, 53824

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OFFSET

0,1

COMMENTS

sopfr(k) = sum of the prime factors of k (with multiplicity).

LINKS

Paolo P. Lava, Table of n, a(n) for n = 0..200

EXAMPLE

sopfr(72) = 2+2+2+3+3 = 12 = 2+2+3+5 = sopfr(72 - sopfr(72)), so 72 is in the sequence.

MATHEMATICA

sopf[n_]:=Module[{sopfn=Total[Times@@@FactorInteger[n]], m}, m=n+sopfn; If[n==m-Total[Times@@@FactorInteger[m]], m, 0]]; DeleteCases[Table[ sopf[n], {n, 55000}], _?(#==0&)] (* Harvey P. Dale, Jun 15 2011 *)

CROSSREFS

Cf. A001414, A050703-A050710, A050780.

Sequence in context: A068899 A053719 A217236 * A060260 A152080 A236769

Adjacent sequences: A050778 A050779 A050780 * A050782 A050783 A050784

KEYWORD

nonn,nice

AUTHOR

Patrick De Geest, Sep 15 1999

EXTENSIONS

Edited by Jon E. Schoenfield, Dec 25 2016

STATUS

approved