21439997 has 2 divisors, whose sum is σ = 21439998. Its totient is φ = 21439996.

The previous prime is 21439987. The next prime is 21440017. The reversal of 21439997 is 79993412.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 17355556 + 4084441 = 4166^2 + 2021^2 .

It is a cyclic number.

It is not a de Polignac number, because 21439997 - 2⁴ = 21439981 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21439927) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10719998 + 10719999.

It is an arithmetic number, because the mean of its divisors is an integer number (10719999).

Almost surely, 2^21439997 is an apocalyptic number.

It is an amenable number.

21439997 is a deficient number, since it is larger than the sum of its proper divisors (1).

21439997 is an equidigital number, since it uses as much as digits as its factorization.

21439997 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 122472, while the sum is 44.

The square root of 21439997 is about 4630.3344371654. The cubic root of 21439997 is about 277.8059693639.

The spelling of 21439997 in words is "twenty-one million, four hundred thirty-nine thousand, nine hundred ninety-seven".