21535644 has 48 divisors (see below), whose sum is σ = 54591488. Its totient is φ = 6568128.

The previous prime is 21535643. The next prime is 21535663. The reversal of 21535644 is 44653512.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21535643) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 19269 + ... + 20355.

Almost surely, 2^21535644 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21535644, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (27295744).

21535644 is an abundant number, since it is smaller than the sum of its proper divisors (33055844).

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

21535644 is a wasteful number, since it uses less digits than its factorization.

21535644 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1234 (or 1232 counting only the distinct ones).

The product of its digits is 14400, while the sum is 30.

The square root of 21535644 is about 4640.6512474005. The cubic root of 21535644 is about 278.2184677479.

The spelling of 21535644 in words is "twenty-one million, five hundred thirty-five thousand, six hundred forty-four".