HP 39gs Master Manual page 100

If the definition is recursive but only involves
value for .
U1(2)
For example, for the sequence
enter the value into
5 U1(1)
The value of will be ignored in the
U1(2)
calculator automatically in the
Convenient screen keys provided
There are a number of very convenient extra buttons provided at the
bottom of the screen when entering sequences.
Two of these - and
moves onto the line (see right). Pressing either will enter the
U(N)
appropriate text into the sequence definition.
The rest become visible once you have begun to enter the sequence
definition.
For example, suppose we enter the Fibonacci sequence into
Rather than having to type all of this we can use the buttons provided, pressing:
This is a very convenient feature, and worth remembering.
There is no mark next to the definition yet, since the sequence is
defined recursively and no values have yet been given for
. Type in a value of
U2(2)
button to switch to the
NUM
As you can see in the screenshot right, the
values in the sequence as a table. If you move the highlight into the
and columns, you can press the
U2
rule. You can experiment for yourself and see the result of pressing the
button (see next page for an example). The
available as usual, but it is easier to use other methods.
rather than both
T
n−1
= T + 3; T = 2
T
n n−1 1
and the expression
U1(N-1)+4
view but filled in by the
SYMB
view.
NUM
- are available as soon as the cursor
for both of these and then press the
1
view.
view shows the actual
NUM
button and see the sequence
and
T T
n−1
you need only
into .
U1(N)
by defining
U2 U2(N)
and
U2(1)
NUM
U1
button is also
100
then you need not enter a
n−2
as
U2(N-1) + U2(N-2)
.