21521647 has 4 divisors (see below), whose sum is σ = 24596176. Its totient is φ = 18447120.

The previous prime is 21521627. The next prime is 21521653. The reversal of 21521647 is 74612512.

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

It is a cyclic number.

It is not a de Polignac number, because 21521647 - 2¹¹ = 21519599 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 (21521627) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1537254 + ... + 1537267.

It is an arithmetic number, because the mean of its divisors is an integer number (6149044).

Almost surely, 2^21521647 is an apocalyptic number.

21521647 is a deficient number, since it is larger than the sum of its proper divisors (3074529).

21521647 is an equidigital number, since it uses as much as digits as its factorization.

21521647 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3074528.

The product of its digits is 3360, while the sum is 28.

The square root of 21521647 is about 4639.1429165310. The cubic root of 21521647 is about 278.1581790489.

The spelling of 21521647 in words is "twenty-one million, five hundred twenty-one thousand, six hundred forty-seven".