21724431 has 8 divisors (see below), whose sum is σ = 28987440. Its totient is φ = 14472192.

The previous prime is 21724427. The next prime is 21724433. The reversal of 21724431 is 13442712.

It is a happy number.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21724431 - 2² = 21724427 is a prime.

It is a super-2 number, since 2×21724431² = 943901804547522, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21724433) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 6721 + ... + 9413.

It is an arithmetic number, because the mean of its divisors is an integer number (3623430).

Almost surely, 2^21724431 is an apocalyptic number.

21724431 is a deficient number, since it is larger than the sum of its proper divisors (7263009).

21724431 is a wasteful number, since it uses less digits than its factorization.

21724431 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5385.

The product of its digits is 1344, while the sum is 24.

The square root of 21724431 is about 4660.9474358761. The cubic root of 21724431 is about 279.0290818980.

It can be divided in two parts, 21724 and 431, that added together give a triangular number (22155 = T₂₁₀).

The spelling of 21724431 in words is "twenty-one million, seven hundred twenty-four thousand, four hundred thirty-one".