21280657 has 4 divisors (see below), whose sum is σ = 21775600. Its totient is φ = 20785716.

The previous prime is 21280639. The next prime is 21280687. The reversal of 21280657 is 75608212.

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 21280657 - 2⁷ = 21280529 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21280687) 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, 247407 + ... + 247492.

It is an arithmetic number, because the mean of its divisors is an integer number (5443900).

Almost surely, 2^21280657 is an apocalyptic number.

It is an amenable number.

21280657 is a deficient number, since it is larger than the sum of its proper divisors (494943).

21280657 is an equidigital number, since it uses as much as digits as its factorization.

21280657 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 494942.

The product of its (nonzero) digits is 6720, while the sum is 31.

The square root of 21280657 is about 4613.0962487249. The cubic root of 21280657 is about 277.1160482877.

Adding to 21280657 its reverse (75608212), we get a palindrome (96888869).

The spelling of 21280657 in words is "twenty-one million, two hundred eighty thousand, six hundred fifty-seven".