21077721 has 24 divisors (see below), whose sum is σ = 35033024. Its totient is φ = 11962080.

The previous prime is 21077659. The next prime is 21077741. The reversal of 21077721 is 12777012.

It is not a de Polignac number, because 21077721 - 2¹⁷ = 20946649 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21077741) 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 23 ways as a sum of consecutive naturals, for example, 8826 + ... + 10956.

Almost surely, 2^21077721 is an apocalyptic number.

21077721 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

It is an amenable number.

21077721 is a deficient number, since it is larger than the sum of its proper divisors (13955303).

21077721 is a wasteful number, since it uses less digits than its factorization.

21077721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2301 (or 2298 counting only the distinct ones).

The product of its (nonzero) digits is 1372, while the sum is 27.

The square root of 21077721 is about 4591.0479195931. The cubic root of 21077721 is about 276.2323578887.

The spelling of 21077721 in words is "twenty-one million, seventy-seven thousand, seven hundred twenty-one".