21002921 has 2 divisors, whose sum is σ = 21002922. Its totient is φ = 21002920.

The previous prime is 21002911. The next prime is 21002929. The reversal of 21002921 is 12920012.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 19536400 + 1466521 = 4420^2 + 1211^2 .

It is a cyclic number.

It is not a de Polignac number, because 21002921 - 2⁶ = 21002857 is a prime.

It is a super-2 number, since 2×21002921² = 882245381064482, which contains 22 as substring.

It is a self number, because there is not a number n which added to its sum of digits gives 21002921.

It is not a weakly prime, because it can be changed into another prime (21002929) 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, 10501460 + 10501461.

It is an arithmetic number, because the mean of its divisors is an integer number (10501461).

Almost surely, 2^21002921 is an apocalyptic number.

It is an amenable number.

21002921 is a deficient number, since it is larger than the sum of its proper divisors (1).

21002921 is an equidigital number, since it uses as much as digits as its factorization.

21002921 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 72, while the sum is 17.

The square root of 21002921 is about 4582.8943911026. The cubic root of 21002921 is about 275.9052088189.

Adding to 21002921 its reverse (12920012), we get a palindrome (33922933).

The spelling of 21002921 in words is "twenty-one million, two thousand, nine hundred twenty-one".