function with parallel iterations

Question

coprimesParallelIter[n_] := DistributeDefinitions[GCD];
ClearAll;
ParallelTable[If[GCD[i, n] == 1, i, Nothing], {i, 1, n - 1}] // 
  Flatten // DeleteCases[Nothing]

That function generates the list of coprimes less than n, but how can this list of coprimes be stored? When I call the function there is no return value.

Answer 1

Clear["Global`*"]

Use a CompoundExpression and store the results in a symbol (note that Nothing evaporates on its own)

coprimesParallelIter[n_] := (
  DistributeDefinitions[GCD];
  ParallelTable[
   If[GCD[i, n] == 1, i, Nothing],
   {i, 1, n - 1}])

list = coprimesParallelIter[20]

(* {1, 3, 7, 9, 11, 13, 17, 19} *)

coprimesParallelIter2[n_] := (
  DistributeDefinitions[GCD];
  ParallelTable[
   If[CoprimeQ[n, i], i, Nothing],
   {i, 1, n - 1}])

list === coprimesParallelIter2[20]

(* True *)