code: function getParent(tile) {
      // top left
      if (tile[0] % 2 === 0 && tile[1] % 2 === 0) {
          return [tile[0] / 2, tile[1] / 2, tile[2] - 1];
      }
      // bottom left
      if ((tile[0] % 2 === 0) && (!tile[1] % 2 === 0)) {
          return [tile[0] / 2, (tile[1] - 1) / 2, tile[2] - 1];
      }
      // top right
      if ((!tile[0] % 2 === 0) && (tile[1] % 2 === 0)) {
          return [(tile[0] - 1) / 2, (tile[1]) / 2, tile[2] - 1];
      }
      // bottom right
      return [(tile[0] - 1) / 2, (tile[1] - 1) / 2, tile[2] - 1];
  }
docs: Get the tile one zoom level lower
  
  @name getParent
  @param {Array<number>} tile
  @returns {Array<number>} tile
  @example
  var tile = getParent([5, 10, 10])
  //=tile