A fan comprising: a hub; and a plurality of blades extending from the hub, wherein each of the plurality of blades comprises: a blade front end having a predetermined curvature; a blade side end extending from the blade front end for forming the lateral side of the blade; and a blade rear end extending from the blade side end, wherein the blade rear end comprises an alternating pattern of ridge parts (610, 620, 650) and groove parts (630, 640), the pattern extending along the edge of the blade rear end, wherein each of the plurality of blades has a positive-pressure surface and a negative-pressure surface opposite to the positive-pressure surface, wherein the ridge parts (610, 620, 650) protrude from the positive-pressure surface and the groove parts (630, 640) protrude from the negative-pressure surface, wherein the alternating pattern comprises: a first upper end part defined between a first ridge part and a second ridge part; a first lower end part defined between a first groove part and a second groove part, the first lower end part being next to the first upper end part; a first connection part extending from the first upper end part of the pattern to the first lower end part of the pattern being next to the first upper end part; and a second connection part extending from a second upper end part of the pattern being next to the first upper end part to the first lower end part of the pattern,wherein a distance between adjacent two of the ridge parts is different from a distance between adjacent two of the groove parts, characterized in that the first connection part and the second connection part have different lengths. a hub; and a plurality of blades extending from the hub, wherein each of the plurality of blades comprises: a blade front end having a predetermined curvature; a blade side end extending from the blade front end for forming the lateral side of the blade; and a blade rear end extending from the blade side end, wherein the blade rear end comprises an alternating pattern of ridge parts (610, 620, 650) and groove parts (630, 640), the pattern extending along the edge of the blade rear end, wherein each of the plurality of blades has a positive-pressure surface and a negative-pressure surface opposite to the positive-pressure surface, wherein the ridge parts (610, 620, 650) protrude from the positive-pressure surface and the groove parts (630, 640) protrude from the negative-pressure surface, wherein the alternating pattern comprises: a first upper end part defined between a first ridge part and a second ridge part; a first lower end part defined between a first groove part and a second groove part, the first lower end part being next to the first upper end part; a first connection part extending from the first upper end part of the pattern to the first lower end part of the pattern being next to the first upper end part; and a second connection part extending from a second upper end part of the pattern being next to the first upper end part to the first lower end part of the pattern,wherein a distance between adjacent two of the ridge parts is different from a distance between adjacent two of the groove parts, a first upper end part defined between a first ridge part and a second ridge part; a first lower end part defined between a first groove part and a second groove part, the first lower end part being next to the first upper end part; a first connection part extending from the first upper end part of the pattern to the first lower end part of the pattern being next to the first upper end part; and a second connection part extending from a second upper end part of the pattern being next to the first upper end part to the first lower end part of the pattern,wherein a distance between adjacent two of the ridge parts is different from a distance between adjacent two of the groove parts, characterized in that the first connection part and the second connection part have different lengths.