OFFSET
1,1
COMMENTS
sopfr(k) = sum of the prime factors of k (with multiplicity).
LINKS
Paolo P. Lava, Table of n, a(n) for n = 1..201 [offset shifted by Georg Fischer, Oct 17 2019]
EXAMPLE
sopfr(39) = 3 + 13 = 16 = 5 + 11 = sopfr(39 + sopfr(39)), so 39 is in the sequence.
MATHEMATICA
sopf[n_] := Total[Apply[Times, FactorInteger[n], {1}]]; ok[n_] := n + sopf[n] - sopf[n + sopf[n]] == n; Select[Range[59200], ok] (* Jean-François Alcover, Apr 18 2011 *)
PROG
(Magma) f:=func<n|&+[j[1]*j[2]: j in Factorization(n)]>; [k:k in [2..60000]| f(k) eq f(k+f(k))]; // Marius A. Burtea, Oct 17 2019
CROSSREFS
KEYWORD
nonn,nice
AUTHOR
Patrick De Geest, Sep 15 1999
EXTENSIONS
Edited by Jon E. Schoenfield, Dec 25 2016
Offset changed to 1 by Jon E. Schoenfield, Oct 17 2019
STATUS
approved