MaplePrimes - answers and comments on Question, Simple problem but can't get it to work

oh yh x,y,z represents

Jabz — Thu, 08 Oct 2009 22:45:28 Z

oh yh x,y,z represents numbers 2,3,7.

i hav tried doing but it dont work am really stuck

for a from 1 to 100 do
    if a:= a / 2 or a/3
        then print(null)
   else     print(a)
   end if;
od;

Hint: modulo

Axel Vogt — Fri, 09 Oct 2009 00:28:10 Z

look up 'mod' in the help and more generally 'modulo' at Wikipedia or a Math book

edited: and if you want a funny way for that homework, than recall Erathostenes'
sieve for primes. Up to 100 you only miss 5 as prime in sqrt(100). So you need
all primes plus multiples of 5 except those bad for 2,3,7

select

alec — Sun, 11 Oct 2009 00:44:19 Z

For example,

select(i->igcd(i,2*3*7)=1,[$1..100])[];

  1, 5, 11, 13, 17, 19, 23, 25, 29, 31, 37, 41, 43, 47, 53, 55, 59,

        61, 65, 67, 71, 73, 79, 83, 85, 89, 95, 97

Alec

Thank u

Jabz — Sun, 11 Oct 2009 18:58:19 Z

Thank u i was trying to use modp(a,b) but didn't succeed. This method seems much easier thank u again.

with modp

alec — Sun, 11 Oct 2009 19:43:45 Z

With modp, that can be done as

remove(i->convert(modp~(i,[2,3,7]),`*`)=0,[$1..100]);

  [1, 5, 11, 13, 17, 19, 23, 25, 29, 31, 37, 41, 43, 47, 53, 55, 59,

        61, 65, 67, 71, 73, 79, 83, 85, 89, 95, 97]

The Eratosthenes sieve (well, not exactly, but a kind of) solution can be done as

{seq(1..100)} minus {seq(seq(i..100,i),i=[2,3,7])};

  {1, 5, 11, 13, 17, 19, 23, 25, 29, 31, 37, 41, 43, 47, 53, 55, 59,

        61, 65, 67, 71, 73, 79, 83, 85, 89, 95, 97}

Alec

Thank u another problem

Jabz — Sun, 11 Oct 2009 20:18:09 Z

I am very grateful 4 ur assistance thank you.

I have a new problem and i am not sure how to tackle it.

Q. Write a procedure to give the factorial of n without using the built in function !.

I am not sure how to implement n*(n-1)*(n-2).......*(n-n) because (n-n) is 0 which will turn everything to 0???