21172824 has 24 divisors (see below), whose sum is σ = 57343260. Its totient is φ = 7057584.

The previous prime is 21172819. The next prime is 21172829. The reversal of 21172824 is 42827112.

It is an interprime number because it is at equal distance from previous prime (21172819) and next prime (21172829).

It is a tau number, because it is divible by the number of its divisors (24).

It is a super-2 number, since 2×21172824² = 896576952269952, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21172829) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 146962 + ... + 147105.

Almost surely, 2^21172824 is an apocalyptic number.

21172824 is a gapful number since it is divisible by the number (24) formed by its first and last digit.

It is an amenable number.

21172824 is an abundant number, since it is smaller than the sum of its proper divisors (36170436).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21172824 is a wasteful number, since it uses less digits than its factorization.

21172824 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 294079 (or 294072 counting only the distinct ones).

The product of its digits is 1792, while the sum is 27.

The square root of 21172824 is about 4601.3937019125. The cubic root of 21172824 is about 276.6471894806.

Adding to 21172824 its reverse (42827112), we get a palindrome (63999936).

The spelling of 21172824 in words is "twenty-one million, one hundred seventy-two thousand, eight hundred twenty-four".