21404665 has 16 divisors (see below), whose sum is σ = 26497296. Its totient is φ = 16588800.

The previous prime is 21404653. The next prime is 21404681. The reversal of 21404665 is 56640412.

It can be written as a sum of positive squares in 8 ways, for example, as 5659641 + 15745024 = 2379^2 + 3968^2 .

It is a de Polignac number, because none of the positive numbers 2^k-21404665 is a prime.

It is a Duffinian number.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 39295 + ... + 39835.

It is an arithmetic number, because the mean of its divisors is an integer number (1656081).

Almost surely, 2^21404665 is an apocalyptic number.

It is an amenable number.

21404665 is a deficient number, since it is larger than the sum of its proper divisors (5092631).

21404665 is a wasteful number, since it uses less digits than its factorization.

21404665 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 780.

The product of its (nonzero) digits is 5760, while the sum is 28.

The square root of 21404665 is about 4626.5175888567. The cubic root of 21404665 is about 277.6532821966.

The spelling of 21404665 in words is "twenty-one million, four hundred four thousand, six hundred sixty-five".