21173921 has 2 divisors, whose sum is σ = 21173922. Its totient is φ = 21173920.

The previous prime is 21173903. The next prime is 21173927. The reversal of 21173921 is 12937112.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 16810000 + 4363921 = 4100^2 + 2089^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21173921 is a prime.

It is not a weakly prime, because it can be changed into another prime (21173927) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10586960 + 10586961.

It is an arithmetic number, because the mean of its divisors is an integer number (10586961).

Almost surely, 2^21173921 is an apocalyptic number.

It is an amenable number.

21173921 is a deficient number, since it is larger than the sum of its proper divisors (1).

21173921 is an equidigital number, since it uses as much as digits as its factorization.

21173921 is an evil number, because the sum of its binary digits is even.

The product of its digits is 756, while the sum is 26.

The square root of 21173921 is about 4601.5129033830. The cubic root of 21173921 is about 276.6519672518.

The spelling of 21173921 in words is "twenty-one million, one hundred seventy-three thousand, nine hundred twenty-one".