Error with the Seed in laravel 5.6

Sorry, I have a question, maybe it's something very simple but I feel like I already locked myself in my mistake and I can not see another solution The question is this:  I have my tables or migrations:  * ranges

  Schema::create('rangos', function (Blueprint $table) {
        $table->increments('id');
        $table->unsignedInteger('inicio');
        $table->unsignedInteger('final');
        $table->timestamps();

    });

* articles

     Schema::create('articulos', function (Blueprint $table) {
        $table->increments('id');
        $table->string('codigo');
        $table->string('SKU');
        $table->string('descripcion',75)->unique();
        $table->double('precioUnitario');
        $table->boolean('a_venta');
        $table->boolean('a_inventario');
        $table->boolean('a_compra');
        $table->boolean('act_fijo');
        $table->string('file',128)->nullable();
        $table->unsignedInteger('id_grupo');
        $table->unsignedInteger('id_area');
        $table->unsignedInteger('id_clase');
        $table->unsignedInteger('id_lista');
        $table->foreign('id_grupo')->references('id')->on('grupos')->onDelete('cascade')->onUpdate('cascade');
        $table->foreign('id_area')->references('id')->on('areas')->onDelete('cascade')->onUpdate('cascade');
        $table->foreign('id_clase')->references('id')->on('clases')->onDelete('cascade')->onUpdate('cascade');
        $table->foreign('id_lista')->references('id')->on('lista_precios')->onDelete('cascade')->onUpdate('cascade');
        $table->timestamps();
    });

* articulo_rango

     Schema::create('articulo_rango', function (Blueprint $table) {
        $table->increments('id');            
        $table->double('precio');
        $table->unsignedInteger('articulo_id');
        $table->unsignedInteger('rango_id');

        $table->timestamps();

        //relaciones
        $table->foreign('articulo_id')->references('id')->on('articulos')->onDelete('cascade')->onUpdate('cascade');
        $table->foreign('rango_id')->references('id')->on('rangos')->onDelete('cascade')->onUpdate('cascade');
    });

Then when making my factory and my seeds

I generate false data but I can not enter what is the price attribute in my database

this is my seed

    factory(App\Articulo::class, 160)->create()->each(function(App\Articulo $articulo){
        $articulo->rango()->attach([
            rand(1,5),
            rand(6,15),
            rand(16, 23),

        ]);
    });

I clarify already believes the belongsToMany

* this is in my model article

   public function rango(){
        return $this->belongsToMany(Rango::class)->withPivot('precio');
    }

* this is in my model range

   public function articulo(){
        return $this->belongsToMany(Articulo::class)->withPivot('precio');
    }

I hope and help me to generate my false data

I'm new to this .. greetings

this is the error