21609997 has 4 divisors (see below), whose sum is σ = 21675616. Its totient is φ = 21544380.

The previous prime is 21609977. The next prime is 21610003. The reversal of 21609997 is 79990612.

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 21609997 - 2⁷ = 21609869 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21609937) 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 3 ways as a sum of consecutive naturals, for example, 32313 + ... + 32974.

It is an arithmetic number, because the mean of its divisors is an integer number (5418904).

Almost surely, 2^21609997 is an apocalyptic number.

It is an amenable number.

21609997 is a deficient number, since it is larger than the sum of its proper divisors (65619).

21609997 is an equidigital number, since it uses as much as digits as its factorization.

21609997 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 65618.

The product of its (nonzero) digits is 61236, while the sum is 43.

The square root of 21609997 is about 4648.6553969938. The cubic root of 21609997 is about 278.5382881712.

The spelling of 21609997 in words is "twenty-one million, six hundred nine thousand, nine hundred ninety-seven".