Arithmetic: a, a+d, a+2d, … (constant difference d)

↳3, 7, 11, 15 → d=4 → next 19

Geometric: a, ar, ar², … (constant ratio r)

↳2, 6, 18, 54 → r=3 → next 162

Fibonacci: 1, 1, 2, 3, 5, 8, 13, … (F_n = F_(n−1) + F_(n−2))

↳1,1,2,3,5,8 → next 13

nth term AP: a + (n−1)d

↳a=4, d=3, n=5 → 4 + 4×3 = 16