21520951 has 4 divisors (see below), whose sum is σ = 21530232. Its totient is φ = 21511672.

The previous prime is 21520949. The next prime is 21520999. The reversal of 21520951 is 15902512.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It is a cyclic number.

It is not a de Polignac number, because 21520951 - 2¹ = 21520949 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 (21520931) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2181 + ... + 6913.

It is an arithmetic number, because the mean of its divisors is an integer number (5382558).

Almost surely, 2^21520951 is an apocalyptic number.

21520951 is a deficient number, since it is larger than the sum of its proper divisors (9281).

21520951 is an equidigital number, since it uses as much as digits as its factorization.

21520951 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 9280.

The product of its (nonzero) digits is 900, while the sum is 25.

The square root of 21520951 is about 4639.0679020683. The cubic root of 21520951 is about 278.1551805148.

The spelling of 21520951 in words is "twenty-one million, five hundred twenty thousand, nine hundred fifty-one".