1256660991 has 12 divisors (see below), whose sum is σ = 1815769800. Its totient is φ = 837500400.

The previous prime is 1256660989. The next prime is 1256661011. The reversal of 1256660991 is 1990666521.

It is a happy number.

It is not a de Polignac number, because 1256660991 - 2¹ = 1256660989 is a prime.

It is a super-2 number, since 2×1256660991² = 3158393692602204162, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1256660971) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 8560 + ... + 50858.

It is an arithmetic number, because the mean of its divisors is an integer number (151314150).

Almost surely, 2^1256660991 is an apocalyptic number.

1256660991 is a deficient number, since it is larger than the sum of its proper divisors (559108809).

1256660991 is a wasteful number, since it uses less digits than its factorization.

1256660991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 45606 (or 45603 counting only the distinct ones).

The product of its (nonzero) digits is 174960, while the sum is 45.

The square root of 1256660991 is about 35449.4145367734. The cubic root of 1256660991 is about 1079.1273789752.

The spelling of 1256660991 in words is "one billion, two hundred fifty-six million, six hundred sixty thousand, nine hundred ninety-one".