21477721 has 4 divisors (see below), whose sum is σ = 21798352. Its totient is φ = 21157092.

The previous prime is 21477697. The next prime is 21477739. The reversal of 21477721 is 12777412.

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 21477721 - 2⁵ = 21477689 is a prime.

It is a super-2 number, since 2×21477721² = 922584998707682, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21477221) 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, 160215 + ... + 160348.

It is an arithmetic number, because the mean of its divisors is an integer number (5449588).

Almost surely, 2^21477721 is an apocalyptic number.

It is an amenable number.

21477721 is a deficient number, since it is larger than the sum of its proper divisors (320631).

21477721 is an equidigital number, since it uses as much as digits as its factorization.

21477721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 320630.

The product of its digits is 5488, while the sum is 31.

The square root of 21477721 is about 4634.4062187081. The cubic root of 21477721 is about 277.9688085012.

The spelling of 21477721 in words is "twenty-one million, four hundred seventy-seven thousand, seven hundred twenty-one".