21659749 has 2 divisors, whose sum is σ = 21659750. Its totient is φ = 21659748.

The previous prime is 21659741. The next prime is 21659777. The reversal of 21659749 is 94795612.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 21622500 + 37249 = 4650^2 + 193^2 .

It is a cyclic number.

It is not a de Polignac number, because 21659749 - 2³ = 21659741 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21659741) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10829874 + 10829875.

It is an arithmetic number, because the mean of its divisors is an integer number (10829875).

Almost surely, 2^21659749 is an apocalyptic number.

It is an amenable number.

21659749 is a deficient number, since it is larger than the sum of its proper divisors (1).

21659749 is an equidigital number, since it uses as much as digits as its factorization.

21659749 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 136080, while the sum is 43.

The square root of 21659749 is about 4654.0035453360. The cubic root of 21659749 is about 278.7518809153.

The spelling of 21659749 in words is "twenty-one million, six hundred fifty-nine thousand, seven hundred forty-nine".