21406457 has 2 divisors, whose sum is σ = 21406458. Its totient is φ = 21406456.

The previous prime is 21406397. The next prime is 21406459. The reversal of 21406457 is 75460412.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 15912121 + 5494336 = 3989^2 + 2344^2 .

It is a cyclic number.

It is not a de Polignac number, because 21406457 - 2⁸ = 21406201 is a prime.

Together with 21406459, it forms a pair of twin primes.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (21406459) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10703228 + 10703229.

It is an arithmetic number, because the mean of its divisors is an integer number (10703229).

Almost surely, 2^21406457 is an apocalyptic number.

It is an amenable number.

21406457 is a deficient number, since it is larger than the sum of its proper divisors (1).

21406457 is an equidigital number, since it uses as much as digits as its factorization.

21406457 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 6720, while the sum is 29.

The square root of 21406457 is about 4626.7112509860. The cubic root of 21406457 is about 277.6610303642.

Adding to 21406457 its reverse (75460412), we get a palindrome (96866869).

The spelling of 21406457 in words is "twenty-one million, four hundred six thousand, four hundred fifty-seven".