21724947 has 6 divisors (see below), whose sum is σ = 31380492. Its totient is φ = 14483292.

The previous prime is 21724943. The next prime is 21724991. The reversal of 21724947 is 74942712.

It is not a de Polignac number, because 21724947 - 2² = 21724943 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21724943) 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, 1206933 + ... + 1206950.

It is an arithmetic number, because the mean of its divisors is an integer number (5230082).

Almost surely, 2^21724947 is an apocalyptic number.

21724947 is a deficient number, since it is larger than the sum of its proper divisors (9655545).

21724947 is a wasteful number, since it uses less digits than its factorization.

21724947 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2413889 (or 2413886 counting only the distinct ones).

The product of its digits is 28224, while the sum is 36.

The square root of 21724947 is about 4661.0027891002. The cubic root of 21724947 is about 279.0312910524.

The spelling of 21724947 in words is "twenty-one million, seven hundred twenty-four thousand, nine hundred forty-seven".