1256121981 has 12 divisors (see below), whose sum is σ = 1815989760. Its totient is φ = 836680200.

The previous prime is 1256121949. The next prime is 1256121983. The reversal of 1256121981 is 1891216521.

1256121981 is a `hidden beast` number, since 1 + 2 + 561 + 2 + 1 + 98 + 1 = 666.

It is not a de Polignac number, because 1256121981 - 2⁵ = 1256121949 is a prime.

It is a super-2 number, since 2×1256121981² = 3155684862302728722, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1256121983) 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, 50271 + ... + 70988.

It is an arithmetic number, because the mean of its divisors is an integer number (151332480).

Almost surely, 2^1256121981 is an apocalyptic number.

It is an amenable number.

1256121981 is a deficient number, since it is larger than the sum of its proper divisors (559867779).

1256121981 is a wasteful number, since it uses less digits than its factorization.

1256121981 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 122416 (or 122413 counting only the distinct ones).

The product of its digits is 8640, while the sum is 36.

The square root of 1256121981 is about 35441.8111980751. The cubic root of 1256121981 is about 1078.9730696229.

The spelling of 1256121981 in words is "one billion, two hundred fifty-six million, one hundred twenty-one thousand, nine hundred eighty-one".