21724819 has 2 divisors, whose sum is σ = 21724820. Its totient is φ = 21724818.

The previous prime is 21724783. The next prime is 21724841. The reversal of 21724819 is 91842712.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21724819 - 2¹³ = 21716627 is a prime.

It is a super-2 number, since 2×21724819² = 943935521165522, which contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (21724019) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10862409 + 10862410.

It is an arithmetic number, because the mean of its divisors is an integer number (10862410).

Almost surely, 2^21724819 is an apocalyptic number.

21724819 is a deficient number, since it is larger than the sum of its proper divisors (1).

21724819 is an equidigital number, since it uses as much as digits as its factorization.

21724819 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 8064, while the sum is 34.

The square root of 21724819 is about 4660.9890581292. The cubic root of 21724819 is about 279.0307430484.

The spelling of 21724819 in words is "twenty-one million, seven hundred twenty-four thousand, eight hundred nineteen".