21605764 has 12 divisors (see below), whose sum is σ = 37933084. Its totient is φ = 10767744.

The previous prime is 21605747. The next prime is 21605777. The reversal of 21605764 is 46750612.

It is a happy number.

It can be written as a sum of positive squares in 2 ways, for example, as 372100 + 21233664 = 610^2 + 4608^2 .

It is a hoax number, since the sum of its digits (31) coincides with the sum of the digits of its distinct prime factors.

It is a congruent number.

It is an unprimeable number.

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 3 ways as a sum of consecutive naturals, for example, 7377 + ... + 9880.

Almost surely, 2^21605764 is an apocalyptic number.

It is an amenable number.

21605764 is a deficient number, since it is larger than the sum of its proper divisors (16327320).

21605764 is a wasteful number, since it uses less digits than its factorization.

21605764 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 17574 (or 17572 counting only the distinct ones).

The product of its (nonzero) digits is 10080, while the sum is 31.

The square root of 21605764 is about 4648.2000817521. The cubic root of 21605764 is about 278.5201001451.

The spelling of 21605764 in words is "twenty-one million, six hundred five thousand, seven hundred sixty-four".