21720894 has 48 divisors (see below), whose sum is σ = 48628224. Its totient is φ = 6458400.

The previous prime is 21720877. The next prime is 21720899. The reversal of 21720894 is 49802712.

It is a happy number.

It is a Smith number, since the sum of its digits (33) coincides with the sum of the digits of its prime factors.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21720899) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 31089 + ... + 31779.

It is an arithmetic number, because the mean of its divisors is an integer number (1013088).

Almost surely, 2^21720894 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21720894, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (24314112).

21720894 is an abundant number, since it is smaller than the sum of its proper divisors (26907330).

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

21720894 is a wasteful number, since it uses less digits than its factorization.

21720894 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 753 (or 740 counting only the distinct ones).

The product of its (nonzero) digits is 8064, while the sum is 33.

The square root of 21720894 is about 4660.5679911358. The cubic root of 21720894 is about 279.0139379735.

The spelling of 21720894 in words is "twenty-one million, seven hundred twenty thousand, eight hundred ninety-four".