21403665 has 12 divisors (see below), whose sum is σ = 37099764. Its totient is φ = 11415264.

The previous prime is 21403643. The next prime is 21403667. The reversal of 21403665 is 56630412.

It can be written as a sum of positive squares in 2 ways, for example, as 15233409 + 6170256 = 3903^2 + 2484^2 .

It is not a de Polignac number, because 21403665 - 2¹¹ = 21401617 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21403667) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 237774 + ... + 237863.

It is an arithmetic number, because the mean of its divisors is an integer number (3091647).

Almost surely, 2^21403665 is an apocalyptic number.

It is an amenable number.

21403665 is a deficient number, since it is larger than the sum of its proper divisors (15696099).

21403665 is a wasteful number, since it uses less digits than its factorization.

21403665 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 475648 (or 475645 counting only the distinct ones).

The product of its (nonzero) digits is 4320, while the sum is 27.

The square root of 21403665 is about 4626.4095149478. The cubic root of 21403665 is about 277.6489582543.

The spelling of 21403665 in words is "twenty-one million, four hundred three thousand, six hundred sixty-five".