N = 7x+1 = 8y+2 = 9z+3, x,y,x integers.
x = (8y+1)/ 7 = y + (y+1)/7
(y+1)/7 = x-y is integer, let (y+1)/7 = m, y=7m-1, x=8m-1, N=56m-6
z=(N-3)/9=(56m-9)/9=6m-1+2m/9
2m/9=z+1-6m is integer, also m is integer, let m=9k,
hence x=72k-1, y=63k-1, z=56k-1, N=504k-6, k can be any integer
Let k=1, you get the minimum N=498.