21185537 has 2 divisors, whose sum is σ = 21185538. Its totient is φ = 21185536.

The previous prime is 21185533. The next prime is 21185539. The reversal of 21185537 is 73558112.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 14508481 + 6677056 = 3809^2 + 2584^2 .

It is a cyclic number.

It is not a de Polignac number, because 21185537 - 2² = 21185533 is a prime.

Together with 21185539, it forms a pair of twin primes.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (21185533) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10592768 + 10592769.

It is an arithmetic number, because the mean of its divisors is an integer number (10592769).

Almost surely, 2^21185537 is an apocalyptic number.

It is an amenable number.

21185537 is a deficient number, since it is larger than the sum of its proper divisors (1).

21185537 is an equidigital number, since it uses as much as digits as its factorization.

21185537 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 8400, while the sum is 32.

The square root of 21185537 is about 4602.7749238910. The cubic root of 21185537 is about 276.7025483695.

The spelling of 21185537 in words is "twenty-one million, one hundred eighty-five thousand, five hundred thirty-seven".