It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also a brilliant number, because the two primes have the same length.
It is a cyclic number.
It is a Duffinian number.
It is a congruent number.
Almost surely, 225556821 is an apocalyptic number.
It is an amenable number.
25556821 is an equidigital number, since it uses as much as digits as its factorization.
25556821 is an odious number, because the sum of its binary digits is odd.
The sum of its prime factors is 10378.
The square root of 25556821 is about 5055.3754558885. The cubic root of 25556821 is about 294.5567258132.
The spelling of 25556821 in words is "twenty-five million, five hundred fifty-six thousand, eight hundred twenty-one".