21901021 has 2 divisors, whose sum is σ = 21901022. Its totient is φ = 21901020.

The previous prime is 21901007. The next prime is 21901051. The reversal of 21901021 is 12010912.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 11978521 + 9922500 = 3461^2 + 3150^2 .

It is a cyclic number.

It is not a de Polignac number, because 21901021 - 2⁹ = 21900509 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21900986 and 21901004.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21901001) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10950510 + 10950511.

It is an arithmetic number, because the mean of its divisors is an integer number (10950511).

Almost surely, 2^21901021 is an apocalyptic number.

It is an amenable number.

21901021 is a deficient number, since it is larger than the sum of its proper divisors (1).

21901021 is an equidigital number, since it uses as much as digits as its factorization.

21901021 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 21901021 is about 4679.8526686211. The cubic root of 21901021 is about 279.7830845504.

Adding to 21901021 its reverse (12010912), we get a palindrome (33911933).

The spelling of 21901021 in words is "twenty-one million, nine hundred one thousand, twenty-one".