 Tribonacci number

Terms of a sequence satisfying the third-order linear recurrence $T_{n+3}=T_n+T_{n+1}+T_{n+2}$. Initial values vary by convention; some counting problems specify $T_1=T_2=T_3=1$. To study divisibility by $m$, retain three consecutive remainders modulo $m$, a deterministic state with at most $m^3$ possibilities.