21085109 has 2 divisors, whose sum is σ = 21085110. Its totient is φ = 21085108.

The previous prime is 21085091. The next prime is 21085123. The reversal of 21085109 is 90158012.

It is a happy number.

Together with previous prime (21085091) it forms an Ormiston pair, because they use the same digits, order apart.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 19166884 + 1918225 = 4378^2 + 1385^2 .

It is a cyclic number.

It is not a de Polignac number, because 21085109 - 2⁸ = 21084853 is a prime.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21085409) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10542554 + 10542555.

It is an arithmetic number, because the mean of its divisors is an integer number (10542555).

Almost surely, 2^21085109 is an apocalyptic number.

It is an amenable number.

21085109 is a deficient number, since it is larger than the sum of its proper divisors (1).

21085109 is an equidigital number, since it uses as much as digits as its factorization.

21085109 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 720, while the sum is 26.

The square root of 21085109 is about 4591.8524584311. The cubic root of 21085109 is about 276.2646283962.

The spelling of 21085109 in words is "twenty-one million, eighty-five thousand, one hundred nine".