21712720 has 20 divisors (see below), whose sum is σ = 50482260. Its totient is φ = 8685056.

The previous prime is 21712697. The next prime is 21712729. The reversal of 21712720 is 2721712.

It can be written as a sum of positive squares in 2 ways, for example, as 12446784 + 9265936 = 3528^2 + 3044^2 .

It is a tau number, because it is divible by the number of its divisors (20).

It is a junction number, because it is equal to n+sod(n) for n = 21712691 and 21712700.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21712729) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 135625 + ... + 135784.

It is an arithmetic number, because the mean of its divisors is an integer number (2524113).

Almost surely, 2^21712720 is an apocalyptic number.

21712720 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21712720 is an abundant number, since it is smaller than the sum of its proper divisors (28769540).

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

21712720 is a wasteful number, since it uses less digits than its factorization.

21712720 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 271422 (or 271416 counting only the distinct ones).

The product of its (nonzero) digits is 392, while the sum is 22.

The square root of 21712720 is about 4659.6909768782. The cubic root of 21712720 is about 278.9789341032.

The spelling of 21712720 in words is "twenty-one million, seven hundred twelve thousand, seven hundred twenty".