21185657 has 2 divisors, whose sum is σ = 21185658. Its totient is φ = 21185656.

The previous prime is 21185651. The next prime is 21185687. The reversal of 21185657 is 75658112.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 21058921 + 126736 = 4589^2 + 356^2 .

It is a cyclic number.

It is not a de Polignac number, because 21185657 - 2⁴ = 21185641 is a prime.

It is not a weakly prime, because it can be changed into another prime (21185651) 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, 10592828 + 10592829.

It is an arithmetic number, because the mean of its divisors is an integer number (10592829).

Almost surely, 2^21185657 is an apocalyptic number.

It is an amenable number.

21185657 is a deficient number, since it is larger than the sum of its proper divisors (1).

21185657 is an equidigital number, since it uses as much as digits as its factorization.

21185657 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 16800, while the sum is 35.

The square root of 21185657 is about 4602.7879594872. The cubic root of 21185657 is about 276.7030708052.

The spelling of 21185657 in words is "twenty-one million, one hundred eighty-five thousand, six hundred fifty-seven".