######################## PROBLÈME 2: #########################

#@# a)
plist := proc(n)
  local i, L;
  L := 2;
  for i from 3 to n by 2 do
    if isprime(i) then L := L,i; fi;
  od;
  [L];
end;

#@# autre:
plist := n -> select( isprime, [seq(i, i=1..n)] );

#@# b)
plist2 := proc(n)
  local i,j, L, T;
  T := array([true$n]);
  L := NULL;
  for i from 2 to n/2 do #@# si $2i>n$ la boucle en $j$ est vide
    if T[i] then
      L := L,i;
      for j from 2*i to n by i do T[j] := false; od
    fi;
  od;
  [L];
end;

#@# un peu plus efficace (construit la liste à la fin):
plist3 := proc(n)
  local i,j, L, T;
  T := array([true$n]);
  for i from 2 to n/2 do
    if T[i] then
      for j from 2*i to n by i do T[j] := false; od
    fi;
  od;
  #@# ne marche apparemment pas dans la version Etudiant, mais est correct
  select(i->T[i], [ seq(i, i=1..n) ]);
end;