21157387 has 2 divisors, whose sum is σ = 21157388. Its totient is φ = 21157386.

The previous prime is 21157373. The next prime is 21157403. The reversal of 21157387 is 78375112.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21157387 - 2¹¹ = 21155339 is a prime.

It is equal to p_1339279 and since 21157387 and 1339279 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 (21157987) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10578693 + 10578694.

It is an arithmetic number, because the mean of its divisors is an integer number (10578694).

Almost surely, 2^21157387 is an apocalyptic number.

21157387 is a deficient number, since it is larger than the sum of its proper divisors (1).

21157387 is an equidigital number, since it uses as much as digits as its factorization.

21157387 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 11760, while the sum is 34.

The square root of 21157387 is about 4599.7159694920. The cubic root of 21157387 is about 276.5799391069.

The spelling of 21157387 in words is "twenty-one million, one hundred fifty-seven thousand, three hundred eighty-seven".