21008564 has 24 divisors (see below), whose sum is σ = 38388168. Its totient is φ = 10050560.

The previous prime is 21008531. The next prime is 21008573. The reversal of 21008564 is 46580012.

It can be written as a sum of positive squares in 4 ways, for example, as 5484964 + 15523600 = 2342^2 + 3940^2 .

It is a super-2 number, since 2×21008564² = 882719522684192, which contains 22 as substring.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 7484 + ... + 9900.

It is an arithmetic number, because the mean of its divisors is an integer number (1599507).

Almost surely, 2^21008564 is an apocalyptic number.

It is an amenable number.

21008564 is a deficient number, since it is larger than the sum of its proper divisors (17379604).

21008564 is a wasteful number, since it uses less digits than its factorization.

21008564 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2515 (or 2513 counting only the distinct ones).

The product of its (nonzero) digits is 1920, while the sum is 26.

The square root of 21008564 is about 4583.5100087160. The cubic root of 21008564 is about 275.9299163929.

Adding to 21008564 its reverse (46580012), we get a palindrome (67588576).

The spelling of 21008564 in words is "twenty-one million, eight thousand, five hundred sixty-four".