21555534 has 128 divisors (see below), whose sum is σ = 60060672. Its totient is φ = 4976640.

The previous prime is 21555511. The next prime is 21555539. The reversal of 21555534 is 43555512.

It is a happy number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21555539) by changing a digit.

It is a polite number, since it can be written in 63 ways as a sum of consecutive naturals, for example, 222174 + ... + 222270.

It is an arithmetic number, because the mean of its divisors is an integer number (469224).

Almost surely, 2^21555534 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21555534, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (30030336).

21555534 is an abundant number, since it is smaller than the sum of its proper divisors (38505138).

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

21555534 is a wasteful number, since it uses less digits than its factorization.

21555534 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 170.

The product of its digits is 15000, while the sum is 30.

The square root of 21555534 is about 4642.7937709961. The cubic root of 21555534 is about 278.3040942030.

It can be divided in two parts, 21 and 555534, that added together give a palindrome (555555).

The spelling of 21555534 in words is "twenty-one million, five hundred fifty-five thousand, five hundred thirty-four".