수학 트릭:
x + y
x - y
x * y
x / y
x * 11
x * x
x = 15, 25, 35, 45, 55, 65 ..
x * 5
x * 9
x * 4
x / 5
1000 - x
x * y
y = 2, 4, 8
2 ^ x
x + y
y = 91 ~ 109, 191 ~ 209, 291 ~ 309 ..
x - y
y = 91 ~ 109, 191 ~ 209, 291 ~ 309 ..
x * y
x,y = 10 ~ 19
x * x
x = 11 ~ 99
x1x2 * y1y2
x1 = y1 = 1 ~ 9, x2 + y2 = 10
23 * 27, 59 * 51, 37 * 33, 68 * 62 ..
x * x
x = 50 ~ 59
x * x
x = 40 ~ 49
x * y
x,y = 11, 21, 31, 41, 51, 61, 71, 81, 91
x% -> y
x * x
x = 100 ~ 109