21901709 has 2 divisors, whose sum is σ = 21901710. Its totient is φ = 21901708.

The previous prime is 21901703. The next prime is 21901739. The reversal of 21901709 is 90710912.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 18679684 + 3222025 = 4322^2 + 1795^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21901709 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21901703) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10950854 + 10950855.

It is an arithmetic number, because the mean of its divisors is an integer number (10950855).

Almost surely, 2^21901709 is an apocalyptic number.

It is an amenable number.

21901709 is a deficient number, since it is larger than the sum of its proper divisors (1).

21901709 is an equidigital number, since it uses as much as digits as its factorization.

21901709 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 1134, while the sum is 29.

The square root of 21901709 is about 4679.9261746314. The cubic root of 21901709 is about 279.7860142274.

The spelling of 21901709 in words is "twenty-one million, nine hundred one thousand, seven hundred nine".