21405124 has 12 divisors (see below), whose sum is σ = 40340524. Its totient is φ = 9879264.

The previous prime is 21405121. The next prime is 21405127. The reversal of 21405124 is 42150412.

It is an interprime number because it is at equal distance from previous prime (21405121) and next prime (21405127).

It can be written as a sum of positive squares in 2 ways, for example, as 1065024 + 20340100 = 1032^2 + 4510^2 .

It is not an unprimeable number, because it can be changed into a prime (21405121) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 205767 + ... + 205870.

Almost surely, 2^21405124 is an apocalyptic number.

It is an amenable number.

21405124 is a deficient number, since it is larger than the sum of its proper divisors (18935400).

21405124 is a wasteful number, since it uses less digits than its factorization.

21405124 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 411654 (or 411652 counting only the distinct ones).

The product of its (nonzero) digits is 320, while the sum is 19.

The square root of 21405124 is about 4626.5671939355. The cubic root of 21405124 is about 277.6552668410.

Adding to 21405124 its reverse (42150412), we get a palindrome (63555536).

The spelling of 21405124 in words is "twenty-one million, four hundred five thousand, one hundred twenty-four".