OFFSET
1,1
COMMENTS
The numbers A100118(n)^3 are in the sequence.
LINKS
Harvey P. Dale, Table of n, a(n) for n = 1..1000
FORMULA
sopfr(n) = 3*p, p prime.
EXAMPLE
44 is in the sequence because 44 = 2^2 * 11 => sum of prime factors = 2*2+11 = 15 = 3*5 where 5 is prime.
MAPLE
with(numtheory):A:= proc(n) local e, j; e := ifactors(n)[2]: add (e[j][1]*e[j][2], j=1..nops(e)) end: for m from 1 to 3000 do: if type(A(m)/3, prime)= true then printf(`%d, `, m):else fi:od:
MATHEMATICA
L = {}; Do[ww = Transpose[FactorInteger[k]]; w = ww[[1]].ww[[2]]; If[PrimeQ[w/3], AppendTo[L, k]], {k, 2, 1000}]; L
Select[Range[700], PrimeQ[Total[Times@@@FactorInteger[#]]/3]&] (* Harvey P. Dale, Nov 23 2022 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Michel Lagneau, Jun 02 2012
STATUS
approved