n= 7 · c + 4
n - 4 ∈ multiplii de 7
n -4 ∈ 7 ,14 ,21,28,35,42,49,56,63,70 ,77 ,84,91 ,98
n ∈ { 11 , 18,25,32,39,46,53,60,67 ,74 ,81,88,95 }
n = 13 ·c + 8
n -8 ∈ multiplii de
n -8 ∈ 104 , 117 , ...... , 13·76=988
n∈ { 112 , 125 ,.........., 996 } sunt 69 numere
