21749309 has 2 divisors, whose sum is σ = 21749310. Its totient is φ = 21749308.

The previous prime is 21749293. The next prime is 21749317. The reversal of 21749309 is 90394712.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 16240900 + 5508409 = 4030^2 + 2347^2 .

It is a cyclic number.

It is not a de Polignac number, because 21749309 - 2⁴ = 21749293 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21749009) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10874654 + 10874655.

It is an arithmetic number, because the mean of its divisors is an integer number (10874655).

Almost surely, 2^21749309 is an apocalyptic number.

It is an amenable number.

21749309 is a deficient number, since it is larger than the sum of its proper divisors (1).

21749309 is an equidigital number, since it uses as much as digits as its factorization.

21749309 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 13608, while the sum is 35.

The square root of 21749309 is about 4663.6154429798. The cubic root of 21749309 is about 279.1355524641.

The spelling of 21749309 in words is "twenty-one million, seven hundred forty-nine thousand, three hundred nine".