1256821 has 2 divisors, whose sum is σ = 1256822. Its totient is φ = 1256820.

The previous prime is 1256819. The next prime is 1256837. The reversal of 1256821 is 1286521.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 1234321 + 22500 = 1111^2 + 150^2 .

It is an emirp because it is prime and its reverse (1286521) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 1256821 - 2¹ = 1256819 is a prime.

Together with 1256819, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1256891) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 628410 + 628411.

It is an arithmetic number, because the mean of its divisors is an integer number (628411).

2^1256821 is an apocalyptic number.

It is an amenable number.

1256821 is a deficient number, since it is larger than the sum of its proper divisors (1).

1256821 is an equidigital number, since it uses as much as digits as its factorization.

1256821 is an evil number, because the sum of its binary digits is even.

The product of its digits is 960, while the sum is 25.

The square root of 1256821 is about 1121.0802825846. The cubic root of 1256821 is about 107.9173178324.

The spelling of 1256821 in words is "one million, two hundred fifty-six thousand, eight hundred twenty-one".