21608538 has 64 divisors (see below), whose sum is σ = 51874560. Its totient is φ = 5870592.

The previous prime is 21608537. The next prime is 21608549. The reversal of 21608538 is 83580612.

It is a happy number.

It is a junction number, because it is equal to n+sod(n) for n = 21608499 and 21608508.

It is not an unprimeable number, because it can be changed into a prime (21608537) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 137556 + ... + 137712.

It is an arithmetic number, because the mean of its divisors is an integer number (810540).

Almost surely, 2^21608538 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21608538, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (25937280).

21608538 is an abundant number, since it is smaller than the sum of its proper divisors (30266022).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21608538 is a wasteful number, since it uses less digits than its factorization.

21608538 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 311.

The product of its (nonzero) digits is 11520, while the sum is 33.

The square root of 21608538 is about 4648.4984672472. The cubic root of 21608538 is about 278.5320195214.

The spelling of 21608538 in words is "twenty-one million, six hundred eight thousand, five hundred thirty-eight".