A2=0 and a2=a 1+a 1 or A2 = A 1+A 1.

Because every term of an is a non-negative real number, then a 1=a2=0.

a3 & gt0，a3=a2+a 1+ 1= 1

A4=a3+a 1=a2+a2= 1 (the landlord should introduce this)

a 100 = a 10+a90(+ 1)，a90=a 10+a80(+ 1)

It will definitely melt in the end.

a 100 = 10 * a 10+n(n & gt； 0, can you understand? )

Because every term of this an is an integer (because the first few terms are only integers)

So this a 10= 1, 2 or 3.

Obviously, a 10 cannot be equal to 1.

Because a10 = a1+A9 (+1) = a1+A2+A7 (+2) = A1+A2+A3+A4 (+3).

Without +3, a 10 is at least equal to a3+a4=2.

Then a10 = a6+a4 (+1) = a3+a3+a4 (+2).

Similarly, a 10 will not be equal to 2.

Then a 10=3.