21345021 has 6 divisors (see below), whose sum is σ = 30831710. Its totient is φ = 14230008.

The previous prime is 21345007. The next prime is 21345029. The reversal of 21345021 is 12054312.

21345021 is a `hidden beast` number, since 213 + 450 + 2 + 1 = 666.

It can be written as a sum of positive squares in only one way, i.e., 17388900 + 3956121 = 4170^2 + 1989^2 .

It is not a de Polignac number, because 21345021 - 2¹⁰ = 21343997 is a prime.

It is a super-3 number, since 3×21345021³ (a number of 23 digits) contains 333 as substring.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21344985 and 21345003.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21345029) 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, 1185826 + ... + 1185843.

Almost surely, 2^21345021 is an apocalyptic number.

It is an amenable number.

21345021 is a deficient number, since it is larger than the sum of its proper divisors (9486689).

21345021 is a wasteful number, since it uses less digits than its factorization.

21345021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2371675 (or 2371672 counting only the distinct ones).

The product of its (nonzero) digits is 240, while the sum is 18.

The square root of 21345021 is about 4620.0672073034. The cubic root of 21345021 is about 277.3951490902.

Adding to 21345021 its reverse (12054312), we get a palindrome (33399333).

The spelling of 21345021 in words is "twenty-one million, three hundred forty-five thousand, twenty-one".