21043457 has 2 divisors, whose sum is σ = 21043458. Its totient is φ = 21043456.

The previous prime is 21043453. The next prime is 21043481. The reversal of 21043457 is 75434012.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 17007376 + 4036081 = 4124^2 + 2009^2 .

It is a cyclic number.

It is not a de Polignac number, because 21043457 - 2² = 21043453 is a prime.

It is equal to p_1332566 and since 21043457 and 1332566 have the same sum of digits, it is a Honaker prime.

It is not a weakly prime, because it can be changed into another prime (21043453) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10521728 + 10521729.

It is an arithmetic number, because the mean of its divisors is an integer number (10521729).

Almost surely, 2^21043457 is an apocalyptic number.

It is an amenable number.

21043457 is a deficient number, since it is larger than the sum of its proper divisors (1).

21043457 is an equidigital number, since it uses as much as digits as its factorization.

21043457 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 3360, while the sum is 26.

The square root of 21043457 is about 4587.3147919017. The cubic root of 21043457 is about 276.0825953530.

Adding to 21043457 its reverse (75434012), we get a palindrome (96477469).

The spelling of 21043457 in words is "twenty-one million, forty-three thousand, four hundred fifty-seven".