21010921 has 2 divisors, whose sum is σ = 21010922. Its totient is φ = 21010920.

The previous prime is 21010909. The next prime is 21010943. The reversal of 21010921 is 12901012.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 19713600 + 1297321 = 4440^2 + 1139^2 .

It is a cyclic number.

It is not a de Polignac number, because 21010921 - 2⁵ = 21010889 is a prime.

It is an alternating number because its digits alternate between even and odd.

It is a junction number, because it is equal to n+sod(n) for n = 21010895 and 21010904.

It is not a weakly prime, because it can be changed into another prime (21010321) 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, 10505460 + 10505461.

It is an arithmetic number, because the mean of its divisors is an integer number (10505461).

Almost surely, 2^21010921 is an apocalyptic number.

It is an amenable number.

21010921 is a deficient number, since it is larger than the sum of its proper divisors (1).

21010921 is an equidigital number, since it uses as much as digits as its factorization.

21010921 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 36, while the sum is 16.

The square root of 21010921 is about 4583.7671188663. The cubic root of 21010921 is about 275.9402350816.

Adding to 21010921 its reverse (12901012), we get a palindrome (33911933).

The spelling of 21010921 in words is "twenty-one million, ten thousand, nine hundred twenty-one".