21256457 has 2 divisors, whose sum is σ = 21256458. Its totient is φ = 21256456.

The previous prime is 21256447. The next prime is 21256471. The reversal of 21256457 is 75465212.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 20214016 + 1042441 = 4496^2 + 1021^2 .

It is a cyclic number.

It is not a de Polignac number, because 21256457 - 2¹⁴ = 21240073 is a prime.

It is not a weakly prime, because it can be changed into another prime (21256447) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10628228 + 10628229.

It is an arithmetic number, because the mean of its divisors is an integer number (10628229).

Almost surely, 2^21256457 is an apocalyptic number.

It is an amenable number.

21256457 is a deficient number, since it is larger than the sum of its proper divisors (1).

21256457 is an equidigital number, since it uses as much as digits as its factorization.

21256457 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 21256457 is about 4610.4725354350. The cubic root of 21256457 is about 277.0109645640.

The spelling of 21256457 in words is "twenty-one million, two hundred fifty-six thousand, four hundred fifty-seven".