21553457 has 6 divisors (see below), whose sum is σ = 21970662. Its totient is φ = 21144032.

The previous prime is 21553453. The next prime is 21553459. The reversal of 21553457 is 75435512.

It can be written as a sum of positive squares in 3 ways, for example, as 8708401 + 12845056 = 2951^2 + 3584^2 .

It is not a de Polignac number, because 21553457 - 2² = 21553453 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21553453) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 1028 + ... + 6645.

It is an arithmetic number, because the mean of its divisors is an integer number (3661777).

Almost surely, 2^21553457 is an apocalyptic number.

It is an amenable number.

21553457 is a deficient number, since it is larger than the sum of its proper divisors (417205).

21553457 is an frugal number, since it uses more digits than its factorization.

21553457 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7779 (or 7726 counting only the distinct ones).

The product of its digits is 21000, while the sum is 32.

The square root of 21553457 is about 4642.5700856314. The cubic root of 21553457 is about 278.2951551811.

Adding to 21553457 its reverse (75435512), we get a palindrome (96988969).

The spelling of 21553457 in words is "twenty-one million, five hundred fifty-three thousand, four hundred fifty-seven".