Integer check with a symbolic variable

So I have:

s=sym('10517669');
p=nextprime(8*(S^4));
if float((p-1)/2)==(p-1)/2
    ...
end

I know float only works for single&double-precision, but p is so large I have to use the symbolic toolbox because it don't want to lose precision.

How could I resolve this?

THANKS

[Fangjun Jiang]

p is accurately represented using sym object in your code. You know p is an integer from theory. What do you try to do? double(p) or single(p) can't represent p without precision loss.

[Yuechuan Chen]

Oh sorry I meant p-1/2 not p...

Answer 1

[Walter Roberson]

if mod(p,1) == 0

[Yuechuan Chen]

Thank you! Didn't think of this erhh

Answer 2

[Fangjun Jiang]

If you want to check whether (p-1)/2 is an integer, then check whether p is an odd number. But since p is a prime number, it seems p is always odd except that p==2.

[Yuechuan Chen]

Of course! Thank you. Didn't realise.