21993356 has 54 divisors (see below), whose sum is σ = 49330764. Its totient is φ = 8484000.

The previous prime is 21993347. The next prime is 21993401. The reversal of 21993356 is 65339912.

It is an unprimeable number.

It is a polite number, since it can be written in 17 ways as a sum of consecutive naturals, for example, 217706 + ... + 217806.

Almost surely, 2^21993356 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 21993356, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (24665382).

21993356 is an abundant number, since it is smaller than the sum of its proper divisors (27337408).

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

21993356 is a wasteful number, since it uses less digits than its factorization.

21993356 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 231 (or 121 counting only the distinct ones).

The product of its digits is 43740, while the sum is 38.

The square root of 21993356 is about 4689.7074535625. The cubic root of 21993356 is about 280.1757230296.

It can be divided in two parts, 2199 and 3356, that added together give a palindrome (5555).

The spelling of 21993356 in words is "twenty-one million, nine hundred ninety-three thousand, three hundred fifty-six".