21608401 has 4 divisors (see below), whose sum is σ = 21618100. Its totient is φ = 21598704.

The previous prime is 21608387. The next prime is 21608417. The reversal of 21608401 is 10480612.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It can be written as a sum of positive squares in 2 ways, for example, as 4601025 + 17007376 = 2145^2 + 4124^2 .

It is a cyclic number.

It is not a de Polignac number, because 21608401 - 2⁵ = 21608369 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21602401) 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, 355 + ... + 6583.

It is an arithmetic number, because the mean of its divisors is an integer number (5404525).

Almost surely, 2^21608401 is an apocalyptic number.

It is an amenable number.

21608401 is a deficient number, since it is larger than the sum of its proper divisors (9699).

21608401 is an equidigital number, since it uses as much as digits as its factorization.

21608401 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9698.

The product of its (nonzero) digits is 384, while the sum is 22.

The square root of 21608401 is about 4648.4837312827. The cubic root of 21608401 is about 278.5314308811.

The spelling of 21608401 in words is "twenty-one million, six hundred eight thousand, four hundred one".