21185557 has 2 divisors, whose sum is σ = 21185558. Its totient is φ = 21185556.

The previous prime is 21185539. The next prime is 21185581. The reversal of 21185557 is 75558112.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 16695396 + 4490161 = 4086^2 + 2119^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21185557 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21185537) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10592778 + 10592779.

It is an arithmetic number, because the mean of its divisors is an integer number (10592779).

Almost surely, 2^21185557 is an apocalyptic number.

It is an amenable number.

21185557 is a deficient number, since it is larger than the sum of its proper divisors (1).

21185557 is an equidigital number, since it uses as much as digits as its factorization.

21185557 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 14000, while the sum is 34.

The square root of 21185557 is about 4602.7770964929. Note that the first 3 decimals coincide. The cubic root of 21185557 is about 276.7026354423.

The spelling of 21185557 in words is "twenty-one million, one hundred eighty-five thousand, five hundred fifty-seven".