21653021 has 8 divisors (see below), whose sum is σ = 23412984. Its totient is φ = 19906560.

The previous prime is 21653011. The next prime is 21653033. The reversal of 21653021 is 12035612.

It can be written as a sum of positive squares in 4 ways, for example, as 11323225 + 10329796 = 3365^2 + 3214^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21653021 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21652984 and 21653002.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21653011) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 101 + ... + 6581.

It is an arithmetic number, because the mean of its divisors is an integer number (2926623).

Almost surely, 2^21653021 is an apocalyptic number.

It is an amenable number.

21653021 is a deficient number, since it is larger than the sum of its proper divisors (1759963).

21653021 is a wasteful number, since it uses less digits than its factorization.

21653021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6751.

The product of its (nonzero) digits is 360, while the sum is 20.

The square root of 21653021 is about 4653.2806706667. The cubic root of 21653021 is about 278.7230157474.

Adding to 21653021 its reverse (12035612), we get a palindrome (33688633).

The spelling of 21653021 in words is "twenty-one million, six hundred fifty-three thousand, twenty-one".