HP 39gs Master Manual page 194

RECURSE
This functions is provided for programmers to let them define functions in
the Sequence aplet.
For example, typing
RECURSE(U,U(N-1)*N,1,2)
produces no useful result in the
result shown right in the
resulting sequence is the factorial numbers.
The syntax is:
RECURSE(<seq.name>,<defn of term n>,<1st term>,<2nd term>)
and it must be stored into a sequence such as
Σ
(<var_name>,<num>,<num>,<expression>)
This function, also available on the keyboard, offers a way of calculating the results of summation notation
problems. The syntax of the function is ordered in the same way as one reads a summation expression (see
the examples below).
5
∑
Eg. 1 which expands to 1
2
i
i =1
can be evaluated using
6
∑
Eg. 2 where x
x
i
i=1
can be evaluated by first defining a list
and then calculating
Note:
Although the variable
each of the cases above, there is nothing special about them.
'i', 'j' & 'k' are simply the letters traditionally used in
mathematical problems involving summation. When working in
the hp 40gs CAS it is not possible to use 'i' because the CAS
will interpret it as
view, but would produce the
HOME
view of the Sequence aplet. The
SYMB
U1,U2..U9,U0
+ 2 + 3 + 4 + 5
2 2 2
(I=1,5,I
= − 2, x = 10, x = 13, x
1 2 3 4
(I=1,6,L1(I))
was used as the summation index in
I
i rather than as a variable name.
seemingly
U1(N)
for it to have any meaning.
giving an answer of 55,
2 2
)
2
= 11, x = − 20, x = 2
5 6
as
L1 {-2,10,13,11,-20,2}
194