(38G) OEIS A262389: Last Digit Composite

09082017, 05:45 AM
(This post was last modified: 09102017 11:33 AM by Gerald H.)
Post: #1




(38G) OEIS A262389: Last Digit Composite
The programme inserts symbolics in the Sequence App to produce the sequence of numbers having rightmost digit composite.
For more info please see https://oeis.org/A262389 Code: RECURSE(U,U2(N2),4,6)►U1(N): 

09132017, 02:06 PM
Post: #2




RE: (38G) OEIS A262389: Last Digit Composite
The 3 recursions can be telescoped into one, producing a faster method of generating the series.
Code: RECURSE(U,IFTE(N>5,U1(N1)+U1(N4)U1(N5),IFTE(N==5,14,IFTE(N==4,9,8))),4,6)►U1(N): Although I find the first version more pretty. 

09132017, 04:06 PM
(This post was last modified: 09132017 04:07 PM by Didier Lachieze.)
Post: #3




RE: (38G) OEIS A262389: Last Digit Composite
Here is a direct formula tested on the Prime as I don't have a 38G:
Code: U(N)=10*IP((N1)/4)+2*(N MOD 4)+7*NOT(N MOD 4)+2 

09132017, 06:09 PM
(This post was last modified: 09142017 05:37 AM by Gerald H.)
Post: #4




RE: (38G) OEIS A262389: Last Digit Composite
Bravo Didier!
On 38G you must have brackets around (NOT(N MOD 4)) then it works OK. I tried a formula, but yours beats mine. Here's mine: Code: RECURSE(U,(5*N+1U2(N)+(3+U2(N))*U2((2*N3U2(N))/4)/2)/2,4,6)►U1(N): just for the record. 

09142017, 06:25 AM
Post: #5




RE: (38G) OEIS A262389: Last Digit Composite
Explicitly, this is what Didier's formula should look like on the 38G:
Code: RECURSE(U,(10*INT((N1)/4)+2*(N MOD 4)+7*NOT N MOD 4)+2 

09142017, 06:45 AM
Post: #6




RE: (38G) OEIS A262389: Last Digit Composite
Didier, perhaps you should inform OEIS of your formula, as it's more elegant than any on their webpage.


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