21173021 has 2 divisors, whose sum is σ = 21173022. Its totient is φ = 21173020.

The previous prime is 21172999. The next prime is 21173029. The reversal of 21173021 is 12037112.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 19456921 + 1716100 = 4411^2 + 1310^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21173021 is a prime.

It is a Sophie Germain prime.

It is a Chen prime.

It is a Curzon number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21173029) 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, 10586510 + 10586511.

It is an arithmetic number, because the mean of its divisors is an integer number (10586511).

Almost surely, 2^21173021 is an apocalyptic number.

It is an amenable number.

21173021 is a deficient number, since it is larger than the sum of its proper divisors (1).

21173021 is an equidigital number, since it uses as much as digits as its factorization.

21173021 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 84, while the sum is 17.

The square root of 21173021 is about 4601.4151084205. The cubic root of 21173021 is about 276.6480474881.

The spelling of 21173021 in words is "twenty-one million, one hundred seventy-three thousand, twenty-one".