21724649 has 2 divisors, whose sum is σ = 21724650. Its totient is φ = 21724648.

The previous prime is 21724621. The next prime is 21724663. The reversal of 21724649 is 94642712.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 20187049 + 1537600 = 4493^2 + 1240^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21724649 is a prime.

It is not a weakly prime, because it can be changed into another prime (21724609) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10862324 + 10862325.

It is an arithmetic number, because the mean of its divisors is an integer number (10862325).

Almost surely, 2^21724649 is an apocalyptic number.

It is an amenable number.

21724649 is a deficient number, since it is larger than the sum of its proper divisors (1).

21724649 is an equidigital number, since it uses as much as digits as its factorization.

21724649 is an evil number, because the sum of its binary digits is even.

The product of its digits is 24192, while the sum is 35.

The square root of 21724649 is about 4660.9708216207. The cubic root of 21724649 is about 279.0300152272.

The spelling of 21724649 in words is "twenty-one million, seven hundred twenty-four thousand, six hundred forty-nine".