addhelp(is, "Is n a term of A048196? I.e. Has Binomial(n, floor(n/2)) the as number of unitary and non-unitary divisors?"); 
is(n) = {my(f = binom(n, n \ 2));
	sqf = 1<<#f; 
	ndiv = prod(i = 1, #f, f[i][2] + 1); 
	sqf << 1 == ndiv
}

addhelp(binom, "List of prime factors of binomial(n, k) with their exponents.")
binom(n, k) = {my(res = List()); 
forprime(p = 2, n, 
	e = val(n, p) - val(n - k, p) - val(k, p); 
	if(e > 0, 
		listput(res, [p, e]~)
	)
); res
}

addhelp(val, "exponent of prime p in n!"); 
val(n, p) = my(r=0); while(n, r+=n\=p);r

fasteris(n) = {
	testbinom(n, n \ 2)
}


testbinom(n, k) = {my(count3 = 0);  
forprime(p = 2, n, 
	e = val(n, p) - val(n - k, p) - val(k, p); 
	if(e > 1, 
		if(e == 3, 
			count3++; 
			if(count3 > 1, 
				return(0)
			)
		,
			return(0); 
		)	
	) 
); count3 == 1
}