21299021 has 6 divisors (see below), whose sum is σ = 22059210. Its totient is φ = 20540576.

The previous prime is 21299017. The next prime is 21299029. The reversal of 21299021 is 12099212.

It is a happy number.

It can be written as a sum of positive squares in 3 ways, for example, as 13402921 + 7896100 = 3661^2 + 2810^2 .

It is not a de Polignac number, because 21299021 - 2² = 21299017 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21299029) 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, 24425 + ... + 25281.

It is an arithmetic number, because the mean of its divisors is an integer number (3676535).

Almost surely, 2^21299021 is an apocalyptic number.

It is an amenable number.

21299021 is a deficient number, since it is larger than the sum of its proper divisors (760189).

21299021 is an frugal number, since it uses more digits than its factorization.

21299021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1743 (or 886 counting only the distinct ones).

The product of its (nonzero) digits is 648, while the sum is 26.

The square root of 21299021 is about 4615.0862397143. The cubic root of 21299021 is about 277.1957371805.

The spelling of 21299021 in words is "twenty-one million, two hundred ninety-nine thousand, twenty-one".