21399649 has 2 divisors, whose sum is σ = 21399650. Its totient is φ = 21399648.

The previous prime is 21399563. The next prime is 21399659. The reversal of 21399649 is 94699312.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 13191424 + 8208225 = 3632^2 + 2865^2 .

It is a cyclic number.

It is not a de Polignac number, because 21399649 - 2⁹ = 21399137 is a prime.

It is not a weakly prime, because it can be changed into another prime (21399659) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10699824 + 10699825.

It is an arithmetic number, because the mean of its divisors is an integer number (10699825).

Almost surely, 2^21399649 is an apocalyptic number.

It is an amenable number.

21399649 is a deficient number, since it is larger than the sum of its proper divisors (1).

21399649 is an equidigital number, since it uses as much as digits as its factorization.

21399649 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 104976, while the sum is 43.

The square root of 21399649 is about 4625.9754646993. The cubic root of 21399649 is about 277.6315919456.

The spelling of 21399649 in words is "twenty-one million, three hundred ninety-nine thousand, six hundred forty-nine".