21305953 has 4 divisors (see below), whose sum is σ = 21525700. Its totient is φ = 21086208.

The previous prime is 21305939. The next prime is 21305983. The reversal of 21305953 is 35950312.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 16908544 + 4397409 = 4112^2 + 2097^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21305953 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21305983) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 109728 + ... + 109921.

It is an arithmetic number, because the mean of its divisors is an integer number (5381425).

Almost surely, 2^21305953 is an apocalyptic number.

It is an amenable number.

21305953 is a deficient number, since it is larger than the sum of its proper divisors (219747).

21305953 is an equidigital number, since it uses as much as digits as its factorization.

21305953 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 219746.

The product of its (nonzero) digits is 4050, while the sum is 28.

The square root of 21305953 is about 4615.8371938360. The cubic root of 21305953 is about 277.2258060496.

The spelling of 21305953 in words is "twenty-one million, three hundred five thousand, nine hundred fifty-three".