7881256661 has 4 divisors (see below), whose sum is σ = 8344860012. Its totient is φ = 7417653312.

The previous prime is 7881256657. The next prime is 7881256673. The reversal of 7881256661 is 1666521887.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 1666521887 = 67 ⋅24873461.

It can be written as a sum of positive squares in 2 ways, for example, as 6173087761 + 1708168900 = 78569^2 + 41330^2 .

It is a cyclic number.

It is not a de Polignac number, because 7881256661 - 2² = 7881256657 is a prime.

It is a super-2 number, since 2×7881256661² (a number of 21 digits) contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (7881256261) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 231801650 + ... + 231801683.

It is an arithmetic number, because the mean of its divisors is an integer number (2086215003).

Almost surely, 2^7881256661 is an apocalyptic number.

It is an amenable number.

7881256661 is a deficient number, since it is larger than the sum of its proper divisors (463603351).

7881256661 is a wasteful number, since it uses less digits than its factorization.

7881256661 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 463603350.

The product of its digits is 967680, while the sum is 50.

The square root of 7881256661 is about 88776.4420384147. The cubic root of 7881256661 is about 1990.0553557323.

The spelling of 7881256661 in words is "seven billion, eight hundred eighty-one million, two hundred fifty-six thousand, six hundred sixty-one".