21397553 has 6 divisors (see below), whose sum is σ = 22583394. Its totient is φ = 20271024.

The previous prime is 21397517. The next prime is 21397559. The reversal of 21397553 is 35579312.

It is a happy number.

It can be written as a sum of positive squares in only one way, i.e., 18601969 + 2795584 = 4313^2 + 1672^2 .

It is not a de Polignac number, because 21397553 - 2⁶ = 21397489 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (21397559) 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, 29276 + ... + 29997.

It is an arithmetic number, because the mean of its divisors is an integer number (3763899).

Almost surely, 2^21397553 is an apocalyptic number.

It is an amenable number.

21397553 is a deficient number, since it is larger than the sum of its proper divisors (1185841).

21397553 is an equidigital number, since it uses as much as digits as its factorization.

21397553 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 59311 (or 59292 counting only the distinct ones).

The product of its digits is 28350, while the sum is 35.

The square root of 21397553 is about 4625.7489123384. The cubic root of 21397553 is about 277.6225273917.

The spelling of 21397553 in words is "twenty-one million, three hundred ninety-seven thousand, five hundred fifty-three".