1256661643 has 4 divisors (see below), whose sum is σ = 1256751288. Its totient is φ = 1256572000.

The previous prime is 1256661631. The next prime is 1256661661. The reversal of 1256661643 is 3461666521.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-1256661643 is a prime.

It is a Smith number, since the sum of its digits (40) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 1256661596 and 1256661605.

It is not an unprimeable number, because it can be changed into a prime (1256661613) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 18733 + ... + 53518.

It is an arithmetic number, because the mean of its divisors is an integer number (314187822).

Almost surely, 2^1256661643 is an apocalyptic number.

1256661643 is a deficient number, since it is larger than the sum of its proper divisors (89645).

1256661643 is an equidigital number, since it uses as much as digits as its factorization.

1256661643 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 89644.

The product of its digits is 155520, while the sum is 40.

The square root of 1256661643 is about 35449.4237329748. The cubic root of 1256661643 is about 1079.1275656049.

The spelling of 1256661643 in words is "one billion, two hundred fifty-six million, six hundred sixty-one thousand, six hundred forty-three".