77765561 has 4 divisors (see below), whose sum is σ = 79662324. Its totient is φ = 75868800.

The previous prime is 77765557. The next prime is 77765563. The reversal of 77765561 is 16556777.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 12559936 + 65205625 = 3544^2 + 8075^2 .

It is a cyclic number.

It is not a de Polignac number, because 77765561 - 2² = 77765557 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (77765563) 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, 948320 + ... + 948401.

It is an arithmetic number, because the mean of its divisors is an integer number (19915581).

Almost surely, 2^77765561 is an apocalyptic number.

It is an amenable number.

77765561 is a deficient number, since it is larger than the sum of its proper divisors (1896763).

77765561 is a wasteful number, since it uses less digits than its factorization.

77765561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1896762.

The product of its digits is 308700, while the sum is 44.

The square root of 77765561 is about 8818.4783834854. The cubic root of 77765561 is about 426.8373711335.

The spelling of 77765561 in words is "seventy-seven million, seven hundred sixty-five thousand, five hundred sixty-one".