21749999 has 2 divisors, whose sum is σ = 21750000. Its totient is φ = 21749998.

The previous prime is 21749989. The next prime is 21750007. The reversal of 21749999 is 99994712.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21749999 - 2²⁰ = 20701423 is a prime.

It is a Sophie Germain prime.

21749999 is a modest number, since divided by 9999 gives 2174 as remainder.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21749929) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10874999 + 10875000.

It is an arithmetic number, because the mean of its divisors is an integer number (10875000).

Almost surely, 2^21749999 is an apocalyptic number.

21749999 is a deficient number, since it is larger than the sum of its proper divisors (1).

21749999 is an equidigital number, since it uses as much as digits as its factorization.

21749999 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 367416, while the sum is 50.

The square root of 21749999 is about 4663.6894193332. The cubic root of 21749999 is about 279.1385043049.

The spelling of 21749999 in words is "twenty-one million, seven hundred forty-nine thousand, nine hundred ninety-nine".