(38G) OEIS A008904: Last NonZero Digit of Factorial

09102017, 04:57 PM
Post: #1




(38G) OEIS A008904: Last NonZero Digit of Factorial
The programme inserts symbolics in the Sequence App to produce the sequence
https://oeis.org/A008904 NB The position indexes in the Sequence App start at 1, while the OEIS starts the sequence at index zero. NB This sequence does NOT become periodic. Code: RECURSE(U,IFTE(N<6,IFTE(N==3,2,IFTE(N==4,6,4)),(IFTE(U3(N)<2,6,IFTE(U3(N)==2,12,IFTE(U3(N)==3,36,IFTE(U3(N)<7,24,IFTE(U3(N)==7,48,IFTE(U3(N)==8,24,36))))))*3^(U2(N) MOD 4)*U1(U2(N)+1)) MOD 10),1,1)►U1(N): 

09112017, 03:54 PM
(This post was last modified: 09112017 04:16 PM by Gerald H.)
Post: #2




RE: (38G) OEIS A008904: Last NonZero Digit of Factorial
A slightly improved version of the programme:
Code: RECURSE(U,IFTE(N<6,IFTE(N==3,2,IFTE(N==4,6,4)),IFTE(U3(N)<2,6,IFTE(U3(N)==2,12,IFTE(U3(N)==3,36,IFTE(U3(N)==7,48,IFTE(U3(N)==9,36,24)))))*3^(U2(N) MOD 4)*U1(U2(N)+1)) MOD 10,1,1)►U1(N): 

09262017, 11:54 AM
(This post was last modified: 09262017 11:59 AM by Gerald H.)
Post: #3




RE: (38G) OEIS A008904: Last NonZero Digit of Factorial
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: 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: 

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