(38G) OEIS A008904: Last Non-Zero Digit of Factorial

[Gerald H]

While the above symbolics work correctly, the recursion takes too long for large input.

Here a programme that takes integer input from the last entry to the stack & returns the result in Ans in the Home screen:

Code:

Ans►N:
IF Ans<2
THEN
1
ELSE
0►C:
0►P:
N:
WHILE Ans
REPEAT
RUN IQUOT5:
R*P+IFTE(R MOD 2,0,R/2)+C►C:
P+1►P:
Q:
END:
2^(C MOD 4):
IF Ans==1
THEN
6:
END:
END:

The programme IQUOT5 takes an integer from the previous calculation & stores the Remainder on division by 5 in R & quotient in Q, returning Q in Ans.

Code:

Ans►Q:
Ans MOD 5►R:
(Q-Ans)/5►Q: