21707720 has 16 divisors (see below), whose sum is σ = 48842460. Its totient is φ = 8683072.

The previous prime is 21707717. The next prime is 21707743. The reversal of 21707720 is 2770712.

It can be written as a sum of positive squares in 2 ways, for example, as 19166884 + 2540836 = 4378^2 + 1594^2 .

It is a self number, because there is not a number n which added to its sum of digits gives 21707720.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 271307 + ... + 271386.

Almost surely, 2^21707720 is an apocalyptic number.

21707720 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21707720 is an abundant number, since it is smaller than the sum of its proper divisors (27134740).

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

21707720 is a wasteful number, since it uses less digits than its factorization.

21707720 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 542704 (or 542700 counting only the distinct ones).

The product of its (nonzero) digits is 1372, while the sum is 26.

The square root of 21707720 is about 4659.1544297222. The cubic root of 21707720 is about 278.9575180583.

The spelling of 21707720 in words is "twenty-one million, seven hundred seven thousand, seven hundred twenty".