21408977 has 4 divisors (see below), whose sum is σ = 21987636. Its totient is φ = 20830320.

The previous prime is 21408973. The next prime is 21408983. The reversal of 21408977 is 77980412.

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 9186961 + 12222016 = 3031^2 + 3496^2 .

It is a cyclic number.

It is not a de Polignac number, because 21408977 - 2² = 21408973 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21408977.

It is not an unprimeable number, because it can be changed into a prime (21408971) 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, 289274 + ... + 289347.

It is an arithmetic number, because the mean of its divisors is an integer number (5496909).

Almost surely, 2^21408977 is an apocalyptic number.

It is an amenable number.

21408977 is a deficient number, since it is larger than the sum of its proper divisors (578659).

21408977 is an equidigital number, since it uses as much as digits as its factorization.

21408977 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 578658.

The product of its (nonzero) digits is 28224, while the sum is 38.

The square root of 21408977 is about 4626.9835746413. The cubic root of 21408977 is about 277.6719254934.

The spelling of 21408977 in words is "twenty-one million, four hundred eight thousand, nine hundred seventy-seven".