21059557 has 2 divisors, whose sum is σ = 21059558. Its totient is φ = 21059556.

The previous prime is 21059537. The next prime is 21059567. The reversal of 21059557 is 75595012.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 12292036 + 8767521 = 3506^2 + 2961^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21059557 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21059537) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10529778 + 10529779.

It is an arithmetic number, because the mean of its divisors is an integer number (10529779).

Almost surely, 2^21059557 is an apocalyptic number.

It is an amenable number.

21059557 is a deficient number, since it is larger than the sum of its proper divisors (1).

21059557 is an equidigital number, since it uses as much as digits as its factorization.

21059557 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 15750, while the sum is 34.

The square root of 21059557 is about 4589.0692956198. The cubic root of 21059557 is about 276.1529861430.

The spelling of 21059557 in words is "twenty-one million, fifty-nine thousand, five hundred fifty-seven".