21720896 has 14 divisors (see below), whose sum is σ = 43102530. Its totient is φ = 10860416.

The previous prime is 21720877. The next prime is 21720899. The reversal of 21720896 is 69802712.

It is a happy number.

It can be written as a sum of positive squares in only one way, i.e., 20430400 + 1290496 = 4520^2 + 1136^2 .

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21720899) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 169631 + ... + 169758.

Almost surely, 2^21720896 is an apocalyptic number.

It is an amenable number.

21720896 is a deficient number, since it is larger than the sum of its proper divisors (21381634).

21720896 is an equidigital number, since it uses as much as digits as its factorization.

21720896 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 339401 (or 339391 counting only the distinct ones).

The product of its (nonzero) digits is 12096, while the sum is 35.

The square root of 21720896 is about 4660.5682057020. The cubic root of 21720896 is about 279.0139465372.

The spelling of 21720896 in words is "twenty-one million, seven hundred twenty thousand, eight hundred ninety-six".