1256639 has 4 divisors (see below), whose sum is σ = 1283424. Its totient is φ = 1229856.

The previous prime is 1256621. The next prime is 1256659. The reversal of 1256639 is 9366521.

It is a happy number.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 9366521 = 1049 ⋅8929.

It is a cyclic number.

It is not a de Polignac number, because 1256639 - 2⁸ = 1256383 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1256659) 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 in 3 ways as a sum of consecutive naturals, for example, 13322 + ... + 13415.

It is an arithmetic number, because the mean of its divisors is an integer number (320856).

2^1256639 is an apocalyptic number.

1256639 is a deficient number, since it is larger than the sum of its proper divisors (26785).

1256639 is an equidigital number, since it uses as much as digits as its factorization.

1256639 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 26784.

The product of its digits is 9720, while the sum is 32.

The square root of 1256639 is about 1120.9991079390. Note that the first 3 decimals coincide. The cubic root of 1256639 is about 107.9121084191.

The spelling of 1256639 in words is "one million, two hundred fifty-six thousand, six hundred thirty-nine".