1256398817 has 4 divisors (see below), whose sum is σ = 1256497200. Its totient is φ = 1256300436.

The previous prime is 1256398789. The next prime is 1256398837. The reversal of 1256398817 is 7188936521.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also a brilliant number, because the two primes have the same length, and also an emirpimes, since its reverse is a distinct semiprime: 7188936521 = 13 ⋅552995117.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-1256398817 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (1256398837) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 26567 + ... + 56732.

It is an arithmetic number, because the mean of its divisors is an integer number (314124300).

Almost surely, 2^1256398817 is an apocalyptic number.

It is an amenable number.

1256398817 is a deficient number, since it is larger than the sum of its proper divisors (98383).

1256398817 is an equidigital number, since it uses as much as digits as its factorization.

1256398817 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 98382.

The product of its digits is 725760, while the sum is 50.

The square root of 1256398817 is about 35445.7164830957. The cubic root of 1256398817 is about 1079.0523285517.

The spelling of 1256398817 in words is "one billion, two hundred fifty-six million, three hundred ninety-eight thousand, eight hundred seventeen".