21405764 has 6 divisors (see below), whose sum is σ = 37460094. Its totient is φ = 10702880.

The previous prime is 21405749. The next prime is 21405773. The reversal of 21405764 is 46750412.

It can be written as a sum of positive squares in only one way, i.e., 21252100 + 153664 = 4610^2 + 392^2 .

It is an unprimeable number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 2675717 + ... + 2675724.

It is an arithmetic number, because the mean of its divisors is an integer number (6243349).

Almost surely, 2^21405764 is an apocalyptic number.

It is an amenable number.

21405764 is a deficient number, since it is larger than the sum of its proper divisors (16054330).

21405764 is a wasteful number, since it uses less digits than its factorization.

21405764 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5351445 (or 5351443 counting only the distinct ones).

The product of its (nonzero) digits is 6720, while the sum is 29.

The square root of 21405764 is about 4626.6363591707. The cubic root of 21405764 is about 277.6580340538.

The spelling of 21405764 in words is "twenty-one million, four hundred five thousand, seven hundred sixty-four".