A characterization of B\"uchi's integer sequences of length 3

We give a new characterization of generalized B\"uchi sequences (sequences whose sequence of squares has constant second difference $(a)$, for some fixed integer $a$) of length 3 over the integers and a strategy for attacking B\"uchi's n Squares Problem. Known characterizations of integer B\"uchi sequences of length 3 are actually characterizations over the rationals, plus some divisibility criterions that keep integer sequences.