21724939 has 2 divisors, whose sum is σ = 21724940. Its totient is φ = 21724938.

The previous prime is 21724931. The next prime is 21724943. The reversal of 21724939 is 93942712.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21724939 - 2³ = 21724931 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21724898 and 21724907.

It is not a weakly prime, because it can be changed into another prime (21724931) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10862469 + 10862470.

It is an arithmetic number, because the mean of its divisors is an integer number (10862470).

Almost surely, 2^21724939 is an apocalyptic number.

21724939 is a deficient number, since it is larger than the sum of its proper divisors (1).

21724939 is an equidigital number, since it uses as much as digits as its factorization.

21724939 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 27216, while the sum is 37.

The square root of 21724939 is about 4661.0019309157. The cubic root of 21724939 is about 279.0312568022.

The spelling of 21724939 in words is "twenty-one million, seven hundred twenty-four thousand, nine hundred thirty-nine".