21721570 has 24 divisors (see below), whose sum is σ = 42341076. Its totient is φ = 8019648.

The previous prime is 21721559. The next prime is 21721577. The reversal of 21721570 is 7512712.

It is a happy number.

It can be written as a sum of positive squares in 6 ways, for example, as 772641 + 20948929 = 879^2 + 4577^2 .

It is not an unprimeable number, because it can be changed into a prime (21721577) by changing a digit.

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 11 ways as a sum of consecutive naturals, for example, 4737 + ... + 8116.

Almost surely, 2^21721570 is an apocalyptic number.

21721570 is a deficient number, since it is larger than the sum of its proper divisors (20619506).

21721570 is a wasteful number, since it uses less digits than its factorization.

21721570 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 12886 (or 12873 counting only the distinct ones).

The product of its (nonzero) digits is 980, while the sum is 25.

The square root of 21721570 is about 4660.6405139208. The cubic root of 21721570 is about 279.0168324441.

The spelling of 21721570 in words is "twenty-one million, seven hundred twenty-one thousand, five hundred seventy".