21003557 has 2 divisors, whose sum is σ = 21003558. Its totient is φ = 21003556.

The previous prime is 21003553. The next prime is 21003589. The reversal of 21003557 is 75530012.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 15476356 + 5527201 = 3934^2 + 2351^2 .

It is a cyclic number.

It is not a de Polignac number, because 21003557 - 2² = 21003553 is a prime.

It is a super-2 number, since 2×21003557² = 882298813304498, which contains 22 as substring.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21003553) 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, 10501778 + 10501779.

It is an arithmetic number, because the mean of its divisors is an integer number (10501779).

Almost surely, 2^21003557 is an apocalyptic number.

It is an amenable number.

21003557 is a deficient number, since it is larger than the sum of its proper divisors (1).

21003557 is an equidigital number, since it uses as much as digits as its factorization.

21003557 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 1050, while the sum is 23.

The square root of 21003557 is about 4582.9637790408. The cubic root of 21003557 is about 275.9079937322.

Adding to 21003557 its reverse (75530012), we get a palindrome (96533569).

The spelling of 21003557 in words is "twenty-one million, three thousand, five hundred fifty-seven".