21173221 has 2 divisors, whose sum is σ = 21173222. Its totient is φ = 21173220.

The previous prime is 21173203. The next prime is 21173231. The reversal of 21173221 is 12237112.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 17969121 + 3204100 = 4239^2 + 1790^2 .

It is a cyclic number.

It is not a de Polignac number, because 21173221 - 2⁹ = 21172709 is a prime.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21173231) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10586610 + 10586611.

It is an arithmetic number, because the mean of its divisors is an integer number (10586611).

Almost surely, 2^21173221 is an apocalyptic number.

It is an amenable number.

21173221 is a deficient number, since it is larger than the sum of its proper divisors (1).

21173221 is an equidigital number, since it uses as much as digits as its factorization.

21173221 is an evil number, because the sum of its binary digits is even.

The product of its digits is 168, while the sum is 19.

The square root of 21173221 is about 4601.4368408140. The cubic root of 21173221 is about 276.6489185563.

The spelling of 21173221 in words is "twenty-one million, one hundred seventy-three thousand, two hundred twenty-one".