21399553 has 4 divisors (see below), whose sum is σ = 24456640. Its totient is φ = 18342468.

The previous prime is 21399551. The next prime is 21399559. The reversal of 21399553 is 35599312.

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.

It is a cyclic number.

It is not a de Polignac number, because 21399553 - 2¹ = 21399551 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21399551) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1528533 + ... + 1528546.

It is an arithmetic number, because the mean of its divisors is an integer number (6114160).

Almost surely, 2^21399553 is an apocalyptic number.

It is an amenable number.

21399553 is a deficient number, since it is larger than the sum of its proper divisors (3057087).

21399553 is an equidigital number, since it uses as much as digits as its factorization.

21399553 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3057086.

The product of its digits is 36450, while the sum is 37.

The square root of 21399553 is about 4625.9650884978. The cubic root of 21399553 is about 277.6311767881.

It can be divided in two parts, 21399 and 553, that added together give a cube (21952 = 28³).

The spelling of 21399553 in words is "twenty-one million, three hundred ninety-nine thousand, five hundred fifty-three".