21697720 has 48 divisors (see below), whose sum is σ = 53673480. Its totient is φ = 7888320.

The previous prime is 21697703. The next prime is 21697721. The reversal of 21697720 is 2779612.

It is a Smith number, since the sum of its digits (34) 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 (21697721) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 2599 + ... + 7081.

Almost surely, 2^21697720 is an apocalyptic number.

21697720 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21697720, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (26836740).

21697720 is an abundant number, since it is smaller than the sum of its proper divisors (31975760).

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

21697720 is a wasteful number, since it uses less digits than its factorization.

21697720 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4516 (or 4501 counting only the distinct ones).

The product of its (nonzero) digits is 10584, while the sum is 34.

The square root of 21697720 is about 4658.0811500016. The cubic root of 21697720 is about 278.9146761009.

It can be divided in two parts, 2169 and 7720, that added together give a palindrome (9889).

The spelling of 21697720 in words is "twenty-one million, six hundred ninety-seven thousand, seven hundred twenty".