77811561 has 6 divisors (see below), whose sum is σ = 112394490. Its totient is φ = 51874368.

The previous prime is 77811551. The next prime is 77811571. The reversal of 77811561 is 16511877.

It is a happy number.

It is an interprime number because it is at equal distance from previous prime (77811551) and next prime (77811571).

It can be written as a sum of positive squares in only one way, i.e., 77105961 + 705600 = 8781^2 + 840^2 .

It is not a de Polignac number, because 77811561 - 2⁵ = 77811529 is a prime.

It is not an unprimeable number, because it can be changed into a prime (77811551) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 4322856 + ... + 4322873.

It is an arithmetic number, because the mean of its divisors is an integer number (18732415).

Almost surely, 2^77811561 is an apocalyptic number.

It is an amenable number.

77811561 is a deficient number, since it is larger than the sum of its proper divisors (34582929).

77811561 is a wasteful number, since it uses less digits than its factorization.

77811561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 8645735 (or 8645732 counting only the distinct ones).

The product of its digits is 11760, while the sum is 36.

The square root of 77811561 is about 8821.0861576112. The cubic root of 77811561 is about 426.9215157029.

The spelling of 77811561 in words is "seventy-seven million, eight hundred eleven thousand, five hundred sixty-one".