21609457 has 4 divisors (see below), whose sum is σ = 21620736. Its totient is φ = 21598180.

The previous prime is 21609439. The next prime is 21609461. The reversal of 21609457 is 75490612.

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, and also a brilliant number, because the two primes have the same length.

It is a cyclic number.

It is not a de Polignac number, because 21609457 - 2¹¹ = 21607409 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21609407) 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, 1969 + ... + 6862.

It is an arithmetic number, because the mean of its divisors is an integer number (5405184).

Almost surely, 2^21609457 is an apocalyptic number.

It is an amenable number.

21609457 is a deficient number, since it is larger than the sum of its proper divisors (11279).

21609457 is an equidigital number, since it uses as much as digits as its factorization.

21609457 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 11278.

The product of its (nonzero) digits is 15120, while the sum is 34.

The square root of 21609457 is about 4648.5973153200. The cubic root of 21609457 is about 278.5359680732.

The spelling of 21609457 in words is "twenty-one million, six hundred nine thousand, four hundred fifty-seven".