77191561 has 4 divisors (see below), whose sum is σ = 79074324. Its totient is φ = 75308800.

The previous prime is 77191559. The next prime is 77191567. The reversal of 77191561 is 16519177.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 16519177 = 139 ⋅118843.

It can be written as a sum of positive squares in 2 ways, for example, as 22505536 + 54686025 = 4744^2 + 7395^2 .

It is not a de Polignac number, because 77191561 - 2¹ = 77191559 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 77191561.

It is not an unprimeable number, because it can be changed into a prime (77191567) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 941320 + ... + 941401.

It is an arithmetic number, because the mean of its divisors is an integer number (19768581).

Almost surely, 2^77191561 is an apocalyptic number.

It is an amenable number.

77191561 is a deficient number, since it is larger than the sum of its proper divisors (1882763).

77191561 is a wasteful number, since it uses less digits than its factorization.

77191561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1882762.

The product of its digits is 13230, while the sum is 37.

The square root of 77191561 is about 8785.8728080937. The cubic root of 77191561 is about 425.7845917364.

The spelling of 77191561 in words is "seventy-seven million, one hundred ninety-one thousand, five hundred sixty-one".