21207997 has 2 divisors, whose sum is σ = 21207998. Its totient is φ = 21207996.

The previous prime is 21207881. The next prime is 21208007. The reversal of 21207997 is 79970212.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 13623481 + 7584516 = 3691^2 + 2754^2 .

It is a cyclic number.

It is not a de Polignac number, because 21207997 - 2⁷ = 21207869 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21201997) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10603998 + 10603999.

It is an arithmetic number, because the mean of its divisors is an integer number (10603999).

Almost surely, 2^21207997 is an apocalyptic number.

It is an amenable number.

21207997 is a deficient number, since it is larger than the sum of its proper divisors (1).

21207997 is an equidigital number, since it uses as much as digits as its factorization.

21207997 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 15876, while the sum is 37.

The square root of 21207997 is about 4605.2141101148. The cubic root of 21207997 is about 276.8002965696.

The spelling of 21207997 in words is "twenty-one million, two hundred seven thousand, nine hundred ninety-seven".