21408004 has 6 divisors (see below), whose sum is σ = 37464014. Its totient is φ = 10704000.

The previous prime is 21408001. The next prime is 21408007. The reversal of 21408004 is 40080412.

It is an interprime number because it is at equal distance from previous prime (21408001) and next prime (21408007).

It can be written as a sum of positive squares in only one way, i.e., 21160000 + 248004 = 4600^2 + 498^2 .

It is not an unprimeable number, because it can be changed into a prime (21408001) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 2675997 + ... + 2676004.

Almost surely, 2^21408004 is an apocalyptic number.

It is an amenable number.

21408004 is a deficient number, since it is larger than the sum of its proper divisors (16056010).

21408004 is a wasteful number, since it uses less digits than its factorization.

21408004 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5352005 (or 5352003 counting only the distinct ones).

The product of its (nonzero) digits is 256, while the sum is 19.

The square root of 21408004 is about 4626.8784293517. The cubic root of 21408004 is about 277.6677188643.

Adding to 21408004 its reverse (40080412), we get a palindrome (61488416).

The spelling of 21408004 in words is "twenty-one million, four hundred eight thousand, four".