21450557 has 4 divisors (see below), whose sum is σ = 21460956. Its totient is φ = 21440160.

The previous prime is 21450553. The next prime is 21450581. The reversal of 21450557 is 75505412.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It can be written as a sum of positive squares in 2 ways, for example, as 2493241 + 18957316 = 1579^2 + 4354^2 .

It is a cyclic number.

It is not a de Polignac number, because 21450557 - 2² = 21450553 is a prime.

It is a super-2 number, since 2×21450557² = 920252791220498, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21450553) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 944 + ... + 6617.

It is an arithmetic number, because the mean of its divisors is an integer number (5365239).

Almost surely, 2^21450557 is an apocalyptic number.

It is an amenable number.

21450557 is a deficient number, since it is larger than the sum of its proper divisors (10399).

21450557 is an equidigital number, since it uses as much as digits as its factorization.

21450557 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10398.

The product of its (nonzero) digits is 7000, while the sum is 29.

The square root of 21450557 is about 4631.4746031907. The cubic root of 21450557 is about 277.8515718194.

Adding to 21450557 its reverse (75505412), we get a palindrome (96955969).

The spelling of 21450557 in words is "twenty-one million, four hundred fifty thousand, five hundred fifty-seven".