(30+1)(30-1)
61*59
199*201
72*68
55^2-45^2
41^2-31^2
76^2-24^2
37^2-23^2

(30+1)(30-1)=30²-1²=900-1=89961*59=359972*68= 489655^2-45^2=55²-45²=3025-2025=100041^2-31^2=41²-31²=1681-961=72076^2-24^2=76²-24²=5776-576=520037^2-23^2=37²-23²=1369-529=840