21806749 has 2 divisors, whose sum is σ = 21806750. Its totient is φ = 21806748.

The previous prime is 21806723. The next prime is 21806803. The reversal of 21806749 is 94760812.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 15960025 + 5846724 = 3995^2 + 2418^2 .

It is a cyclic number.

It is not a de Polignac number, because 21806749 - 2⁷ = 21806621 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21806149) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10903374 + 10903375.

It is an arithmetic number, because the mean of its divisors is an integer number (10903375).

Almost surely, 2^21806749 is an apocalyptic number.

It is an amenable number.

21806749 is a deficient number, since it is larger than the sum of its proper divisors (1).

21806749 is an equidigital number, since it uses as much as digits as its factorization.

21806749 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 24192, while the sum is 37.

The square root of 21806749 is about 4669.7696945353. The cubic root of 21806749 is about 279.3810691059.

The spelling of 21806749 in words is "twenty-one million, eight hundred six thousand, seven hundred forty-nine".