21456257 has 2 divisors, whose sum is σ = 21456258. Its totient is φ = 21456256.

The previous prime is 21456251. The next prime is 21456287. The reversal of 21456257 is 75265412.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 16032016 + 5424241 = 4004^2 + 2329^2 .

It is a cyclic number.

It is not a de Polignac number, because 21456257 - 2¹² = 21452161 is a prime.

It is not a weakly prime, because it can be changed into another prime (21456251) 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, 10728128 + 10728129.

It is an arithmetic number, because the mean of its divisors is an integer number (10728129).

Almost surely, 2^21456257 is an apocalyptic number.

It is an amenable number.

21456257 is a deficient number, since it is larger than the sum of its proper divisors (1).

21456257 is an equidigital number, since it uses as much as digits as its factorization.

21456257 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 16800, while the sum is 32.

The square root of 21456257 is about 4632.0899170893. The cubic root of 21456257 is about 277.8761805619.

The spelling of 21456257 in words is "twenty-one million, four hundred fifty-six thousand, two hundred fifty-seven".