21042997 has 2 divisors, whose sum is σ = 21042998. Its totient is φ = 21042996.

The previous prime is 21042979. The next prime is 21043007. The reversal of 21042997 is 79924012.

It is a happy number.

Together with previous prime (21042979) it forms an Ormiston pair, because they use the same digits, order apart.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 17690436 + 3352561 = 4206^2 + 1831^2 .

It is a cyclic number.

It is not a de Polignac number, because 21042997 - 2¹⁵ = 21010229 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21042947) 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, 10521498 + 10521499.

It is an arithmetic number, because the mean of its divisors is an integer number (10521499).

Almost surely, 2^21042997 is an apocalyptic number.

It is an amenable number.

21042997 is a deficient number, since it is larger than the sum of its proper divisors (1).

21042997 is an equidigital number, since it uses as much as digits as its factorization.

21042997 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 9072, while the sum is 34.

The square root of 21042997 is about 4587.2646533637. The cubic root of 21042997 is about 276.0805836601.

The spelling of 21042997 in words is "twenty-one million, forty-two thousand, nine hundred ninety-seven".