x:31=c rest 13
x=31c+13
x-13=31c+13-13
x-13=31c
x-13∈M31
M31={31,62,93,124,155,186,217,248,279....}
x-13=93
x=93+13
x=106
106:31=3 rest 13 e bun
x-13=124⇒x=137
137:31=4 rest 13
x-13=155⇒x=168
168:31=5 rest13
x-13=186⇒x=199
199:31=6 rest 13
nr.sunt:106,137,168,199.......
