21809693 has 2 divisors, whose sum is σ = 21809694. Its totient is φ = 21809692.

The previous prime is 21809677. The next prime is 21809719. The reversal of 21809693 is 39690812.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 18207289 + 3602404 = 4267^2 + 1898^2 .

It is a cyclic number.

It is not a de Polignac number, because 21809693 - 2⁴ = 21809677 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21809633) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10904846 + 10904847.

It is an arithmetic number, because the mean of its divisors is an integer number (10904847).

Almost surely, 2^21809693 is an apocalyptic number.

It is an amenable number.

21809693 is a deficient number, since it is larger than the sum of its proper divisors (1).

21809693 is an equidigital number, since it uses as much as digits as its factorization.

21809693 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 23328, while the sum is 38.

The square root of 21809693 is about 4670.0849028685. The cubic root of 21809693 is about 279.3936410679.

The spelling of 21809693 in words is "twenty-one million, eight hundred nine thousand, six hundred ninety-three".