21523421 has 2 divisors, whose sum is σ = 21523422. Its totient is φ = 21523420.

The previous prime is 21523417. The next prime is 21523433. The reversal of 21523421 is 12432512.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 10797796 + 10725625 = 3286^2 + 3275^2 .

It is a cyclic number.

It is not a de Polignac number, because 21523421 - 2² = 21523417 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21523393 and 21523402.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21553421) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10761710 + 10761711.

It is an arithmetic number, because the mean of its divisors is an integer number (10761711).

Almost surely, 2^21523421 is an apocalyptic number.

It is an amenable number.

21523421 is a deficient number, since it is larger than the sum of its proper divisors (1).

21523421 is an equidigital number, since it uses as much as digits as its factorization.

21523421 is an evil number, because the sum of its binary digits is even.

The product of its digits is 480, while the sum is 20.

The square root of 21523421 is about 4639.3341117018. The cubic root of 21523421 is about 278.1658215720.

Adding to 21523421 its reverse (12432512), we get a palindrome (33955933).

Subtracting from 21523421 its reverse (12432512), we obtain a palindrome (9090909).

The spelling of 21523421 in words is "twenty-one million, five hundred twenty-three thousand, four hundred twenty-one".