The square of A=n+15n+26 is a complete square number. Let a = n 2+ 15n+26 = k 2 (k is a natural number) n 2+ 15n+26-k 2 = 0 (n+65438).

4k 2+ 12 1 is a complete square number. 4k 2 is a complete square number, liuking 123.

Because 4k 2+4k+1= (2k+1) 2 is equal to121= 4k+1k = 30.

Liu Jin 123

(2n+ 15)^2=

4k^2+ 12 1=372 1=6 1^2

2n+ 15 = 6 1 . n = 23 . Liu king 123