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A050781 Numbers k such that sopfr(k) = sopfr(k - sopfr(k)). 4
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 (list; graph; refs; listen; history; text; internal format)
OFFSET
0,1
COMMENTS
sopfr(k) = sum of the prime factors of k (with multiplicity).
LINKS
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
Sequence in context: A068899 A053719 A217236 * A060260 A152080 A236769
KEYWORD
nonn,nice
AUTHOR
Patrick De Geest, Sep 15 1999
EXTENSIONS
Edited by Jon E. Schoenfield, Dec 25 2016
STATUS
approved

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Last modified May 22 06:48 EDT 2024. Contains 372743 sequences. (Running on oeis4.)