21289913 has 2 divisors, whose sum is σ = 21289914. Its totient is φ = 21289912.

The previous prime is 21289907. The next prime is 21289949. The reversal of 21289913 is 31998212.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 19123129 + 2166784 = 4373^2 + 1472^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21289913 is a prime.

It is a Sophie Germain prime.

It is a Curzon number.

It is not a weakly prime, because it can be changed into another prime (21289993) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10644956 + 10644957.

It is an arithmetic number, because the mean of its divisors is an integer number (10644957).

Almost surely, 2^21289913 is an apocalyptic number.

It is an amenable number.

21289913 is a deficient number, since it is larger than the sum of its proper divisors (1).

21289913 is an equidigital number, since it uses as much as digits as its factorization.

21289913 is an evil number, because the sum of its binary digits is even.

The product of its digits is 7776, while the sum is 35.

The square root of 21289913 is about 4614.0993704081. The cubic root of 21289913 is about 277.1562195780.

The spelling of 21289913 in words is "twenty-one million, two hundred eighty-nine thousand, nine hundred thirteen".