21000557 has 2 divisors, whose sum is σ = 21000558. Its totient is φ = 21000556.

The previous prime is 21000533. The next prime is 21000563. The reversal of 21000557 is 75500012.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 20529961 + 470596 = 4531^2 + 686^2 .

It is a cyclic number.

It is not a de Polignac number, because 21000557 - 2¹² = 20996461 is a prime.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21000517) by changing a digit.

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

It is a good prime.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10500278 + 10500279.

It is an arithmetic number, because the mean of its divisors is an integer number (10500279).

Almost surely, 2^21000557 is an apocalyptic number.

It is an amenable number.

21000557 is a deficient number, since it is larger than the sum of its proper divisors (1).

21000557 is an equidigital number, since it uses as much as digits as its factorization.

21000557 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 350, while the sum is 20.

The square root of 21000557 is about 4582.6364682353. The cubic root of 21000557 is about 275.8948568559.

Adding to 21000557 its reverse (75500012), we get a palindrome (96500569).

The spelling of 21000557 in words is "twenty-one million, five hundred fifty-seven", and thus it is an aban number.