21090913 has 2 divisors, whose sum is σ = 21090914. Its totient is φ = 21090912.

The previous prime is 21090899. The next prime is 21090919. The reversal of 21090913 is 31909012.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 19421649 + 1669264 = 4407^2 + 1292^2 .

It is a cyclic number.

It is not a de Polignac number, because 21090913 - 2⁹ = 21090401 is a prime.

It is a super-2 number, since 2×21090913² = 889653222347138, which contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (21090919) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10545456 + 10545457.

It is an arithmetic number, because the mean of its divisors is an integer number (10545457).

Almost surely, 2^21090913 is an apocalyptic number.

It is an amenable number.

21090913 is a deficient number, since it is larger than the sum of its proper divisors (1).

21090913 is an equidigital number, since it uses as much as digits as its factorization.

21090913 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 486, while the sum is 25.

The square root of 21090913 is about 4592.4844038930. The cubic root of 21090913 is about 276.2899747643.

Adding to 21090913 its reverse (31909012), we get a palindrome (52999925).

The spelling of 21090913 in words is "twenty-one million, ninety thousand, nine hundred thirteen".