Matti's CS Notebook

1.0. Definition of a difference equation

1 The difference table for sequences

$$ \begin{array}{r l} (\text{i}) & 0, 2, 6, 12, 20, 30, 42, 56, \ldots \\ (\text{ii}) & 0, 4, 18, 48, 100, 180, 294, \ldots \\ (\text{iii}) & 1, 3, 19, 85, 261, 631, \ldots \\ \end{array} $$

are,

\( \begin{array}{ r c c c c } (\text{i}): & & & & \\[0.0em] 0 & & & & \\[0.0em] & \searrow & & & \\[0.0em] & & 2 - 0 = 2 & & \\[0.0em] & \nearrow & & \searrow & \\[0.0em] 2 & & & & 4 - 2 = 2 \\[0.0em] & \searrow & & \nearrow & \\[0.0em] & & 6 - 2 = 4 & & \\[0.0em] & \nearrow & & \searrow & \\[0.0em] 6 & & & & 6 - 4 = 2 \\[0.0em] & \searrow & & \nearrow & \\[0.0em] & & 12 - 6 = 6 & & \\[0.0em] & \nearrow & & \searrow & \\[0.0em] 12 & & & & 8 - 6 = 2 \\[0.0em] & \searrow & & \nearrow & \\[0.0em] & & 20 - 12 = 8 & & \\[0.0em] & \nearrow & & \searrow & \\[0.0em] 20 & & & & 10 - 8 = 2 \\[0.0em] & \searrow & & \nearrow & \\[0.0em] & & 30 - 20 = 10 & & \\[0.0em] & \nearrow & & \searrow & \\[0.0em] 30 & & & & 12 - 10 = 2 \\[0.0em] & \searrow & & \nearrow & \\[0.0em] & & 42 - 30 = 12 & & \\[0.0em] & \nearrow & & \searrow & \\[0.0em] 42 & & & & 14 - 12 = 2 \\[0.0em] & \searrow & & \nearrow & \\[0.0em] & & 56 - 42 = 14 & & \\[0.0em] & \nearrow & & & \\[0.0em] 56 & & & & \\[0.0em] \end{array} \)
\( \begin{array}{ r c c c c } (\text{ii}): & & & & & & \\[0.0em] 0 & & & & & & \\[0.0em] & \searrow & & & & & \\[0.0em] & & 4 - 0 = 4 & & & & \\[0.0em] & \nearrow & & \searrow & & & \\[0.0em] 4 & & & & 14 - 4 = 10 & & \\[0.0em] & \searrow & & \nearrow & & \searrow & \\[0.0em] & & 18 - 4 = 14 & & & & 16 - 10 = 6 \\[0.0em] & \nearrow & & \searrow & & \nearrow & \\[0.0em] 18 & & & & 30 - 14 = 16 & & \\[0.0em] & \searrow & & \nearrow & & \searrow & \\[0.0em] & & 48 - 18 = 30 & & & & 22 - 16 = 6 \\[0.0em] & \nearrow & & \searrow & & \nearrow & \\[0.0em] 48 & & & & 52 - 30 = 22 & & \\[0.0em] & \searrow & & \nearrow & & \searrow & \\[0.0em] & & 100 - 48 = 52 & & & & 28 - 22 = 6 \\[0.0em] & \nearrow & & \searrow & & \nearrow & \\[0.0em] 100 & & & & 80 - 52 = 28 & & \\[0.0em] & \searrow & & \nearrow & & \searrow & \\[0.0em] & & 180 - 100 = 80 & & & & 34 - 28 = 6 \\[0.0em] & \nearrow & & \searrow & & \nearrow & \\[0.0em] 180 & & & & 114 - 80 = 34 & & \\[0.0em] & \searrow & & & & & \\[0.0em] & & 294 - 180 = 114 & & & & \\[0.0em] & \nearrow & & & & & \\[0.0em] 294 & & & & & & \\[0.0em] \end{array} \)
\( \begin{array}{ r c c c c } (\text{iii}): & & & & & & & & & & \\[0.0em] 1 & & & & & & & & & & \\[0.0em] & \searrow & & & & & & & & & \\[0.0em] & & 3 - 1 = 3 & & & & & & & & \\[0.0em] & \nearrow & & \searrow & & & & & & & \\[0.0em] 3 & & & & 16 - 3 = 13 & & & & & & \\[0.0em] & \searrow & & \nearrow & & \searrow & & & & & \\[0.0em] & & 19 - 3 = 16 & & & & 50 - 13 = 37 & & & & \\[0.0em] & \nearrow & & \searrow & & \nearrow & & \searrow & & & \\[0.0em] 19 & & & & 66 - 16 = 50 & & & & 50 - 37 = 13 & & \\[0.0em] & \searrow & & \nearrow & & \searrow & & \nearrow & & \searrow & \\[0.0em] & & 85 - 19 = 66 & & & & 110 - 50 = 60 & & & & 189 \\[0.0em] & \nearrow & & \searrow & & \nearrow & & \searrow & & \nearrow & \\[0.0em] 85 & & & & 176 - 66 = 110 & & & & 262 - 60 = 202 & & \\[0.0em] & \searrow & & \nearrow & & \searrow & & \nearrow & & & \\[0.0em] & & 261 - 85 = 176 & & & & 372 - 110 = 262 & & & & \\[0.0em] & \nearrow & & \searrow & & \nearrow & & & & & \\[0.0em] 261 & & & & 631 - 261 = 372 & & & & & & \\[0.0em] & \searrow & & \nearrow & & & & & & & \\[0.0em] & & 631 - 261 = 370 & & & & & & & & \\[0.0em] & \nearrow & & & & & & & & & \\[0.0em] 631 & & & & & & & & & & \\[0.0em] \end{array} \)