21405224 has 8 divisors (see below), whose sum is σ = 40134810. Its totient is φ = 10702608.

The previous prime is 21405187. The next prime is 21405247. The reversal of 21405224 is 42250412.

It is a happy number.

It can be written as a sum of positive squares in only one way, i.e., 18576100 + 2829124 = 4310^2 + 1682^2 .

It is a tau number, because it is divible by the number of its divisors (8).

It is a super-2 number, since 2×21405224² = 916367228980352, which contains 22 as substring.

It is a junction number, because it is equal to n+sod(n) for n = 21405196 and 21405205.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 1337819 + ... + 1337834.

Almost surely, 2^21405224 is an apocalyptic number.

It is an amenable number.

21405224 is a deficient number, since it is larger than the sum of its proper divisors (18729586).

21405224 is a wasteful number, since it uses less digits than its factorization.

21405224 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2675659 (or 2675655 counting only the distinct ones).

The product of its (nonzero) digits is 640, while the sum is 20.

The square root of 21405224 is about 4626.5780010716. The cubic root of 21405224 is about 277.6556992216.

Adding to 21405224 its reverse (42250412), we get a palindrome (63655636).

The spelling of 21405224 in words is "twenty-one million, four hundred five thousand, two hundred twenty-four".