21809393 has 2 divisors, whose sum is σ = 21809394. Its totient is φ = 21809392.

The previous prime is 21809377. The next prime is 21809401. The reversal of 21809393 is 39390812.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 18809569 + 2999824 = 4337^2 + 1732^2 .

It is a cyclic number.

It is not a de Polignac number, because 21809393 - 2⁴ = 21809377 is a prime.

It is equal to p_1377926 and since 21809393 and 1377926 have the same sum of digits, it is a Honaker prime.

It is not a weakly prime, because it can be changed into another prime (21809303) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10904696 + 10904697.

It is an arithmetic number, because the mean of its divisors is an integer number (10904697).

Almost surely, 2^21809393 is an apocalyptic number.

It is an amenable number.

21809393 is a deficient number, since it is larger than the sum of its proper divisors (1).

21809393 is an equidigital number, since it uses as much as digits as its factorization.

21809393 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 11664, while the sum is 35.

The square root of 21809393 is about 4670.0527834276. The cubic root of 21809393 is about 279.3923600094.

The spelling of 21809393 in words is "twenty-one million, eight hundred nine thousand, three hundred ninety-three".