21547421 has 4 divisors (see below), whose sum is σ = 24625632. Its totient is φ = 18469212.

The previous prime is 21547411. The next prime is 21547433. The reversal of 21547421 is 12474512.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21547421 - 2²² = 17353117 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 (21547411) 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, 1539095 + ... + 1539108.

It is an arithmetic number, because the mean of its divisors is an integer number (6156408).

Almost surely, 2^21547421 is an apocalyptic number.

It is an amenable number.

21547421 is a deficient number, since it is larger than the sum of its proper divisors (3078211).

21547421 is an equidigital number, since it uses as much as digits as its factorization.

21547421 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3078210.

The product of its digits is 2240, while the sum is 26.

The square root of 21547421 is about 4641.9199691507. The cubic root of 21547421 is about 278.2691740993.

The spelling of 21547421 in words is "twenty-one million, five hundred forty-seven thousand, four hundred twenty-one".