How to apply a function on a number which is in 'sym' format?

p = sym('2')^100 - 15;
results =  p_inverse(p-1, p);

where the function p_inverse is defined as;

function ia = p_inverse(a, p)
[~,ia] = gcd(a,p);
end

How can I find p_inverse for such p as defined above?

Answer 1

[Walter Roberson]

p = sym('2')^100 - 15;
results =  p_inverse(p-1, p)

results = 

1267650600228229401496703205360

mod(results * (p-1),p)

ans = 

1

function inv = p_inverse(a, p)
    [~, ia] = gcd(a,p);
    inv = mod(ia, p);
end