256121781987 has 8 divisors (see below), whose sum is σ = 341528806080. Its totient is φ = 170731306280.

The previous prime is 256121781947. The next prime is 256121781989. The reversal of 256121781987 is 789187121652.

It is a happy number.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 256121781987 - 2⁷ = 256121781859 is a prime.

It is not an unprimeable number, because it can be changed into a prime (256121781989) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 4100937 + ... + 4162922.

It is an arithmetic number, because the mean of its divisors is an integer number (42691100760).

Almost surely, 2^256121781987 is an apocalyptic number.

256121781987 is a deficient number, since it is larger than the sum of its proper divisors (85407024093).

256121781987 is a wasteful number, since it uses less digits than its factorization.

256121781987 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 8274193.

The product of its digits is 3386880, while the sum is 57.

The spelling of 256121781987 in words is "two hundred fifty-six billion, one hundred twenty-one million, seven hundred eighty-one thousand, nine hundred eighty-seven".