21020161 has 2 divisors, whose sum is σ = 21020162. Its totient is φ = 21020160.

The previous prime is 21020159. The next prime is 21020227. The reversal of 21020161 is 16102012.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 20875761 + 144400 = 4569^2 + 380^2 .

It is a cyclic number.

It is not a de Polignac number, because 21020161 - 2¹ = 21020159 is a prime.

Together with 21020159, it forms a pair of twin primes.

It is not a weakly prime, because it can be changed into another prime (21020761) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10510080 + 10510081.

It is an arithmetic number, because the mean of its divisors is an integer number (10510081).

Almost surely, 2^21020161 is an apocalyptic number.

It is an amenable number.

21020161 is a deficient number, since it is larger than the sum of its proper divisors (1).

21020161 is an equidigital number, since it uses as much as digits as its factorization.

21020161 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 24, while the sum is 13.

The square root of 21020161 is about 4584.7749126866. The cubic root of 21020161 is about 275.9806793519.

Adding to 21020161 its reverse (16102012), we get a palindrome (37122173).

The spelling of 21020161 in words is "twenty-one million, twenty thousand, one hundred sixty-one".