77720781 has 4 divisors (see below), whose sum is σ = 103627712. Its totient is φ = 51813852.

The previous prime is 77720761. The next prime is 77720791. The reversal of 77720781 is 18702777.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also an emirpimes, since its reverse is a distinct semiprime: 18702777 = 3 ⋅6234259.

It is not a de Polignac number, because 77720781 - 2¹⁰ = 77719757 is a prime.

It is a super-2 number, since 2×77720781² = 12081039598499922, which contains 22 as substring.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (77720701) 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, 12953461 + ... + 12953466.

It is an arithmetic number, because the mean of its divisors is an integer number (25906928).

Almost surely, 2^77720781 is an apocalyptic number.

It is an amenable number.

77720781 is a deficient number, since it is larger than the sum of its proper divisors (25906931).

77720781 is a wasteful number, since it uses less digits than its factorization.

77720781 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 25906930.

The product of its (nonzero) digits is 38416, while the sum is 39.

The square root of 77720781 is about 8815.9390310959. The cubic root of 77720781 is about 426.7554263447.

The spelling of 77720781 in words is "seventy-seven million, seven hundred twenty thousand, seven hundred eighty-one".