77665721 has 4 divisors (see below), whose sum is σ = 88760832. Its totient is φ = 66570612.

The previous prime is 77665717. The next prime is 77665727. The reversal of 77665721 is 12756677.

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: 12756677 = 73 ⋅174749.

It is a cyclic number.

It is not a de Polignac number, because 77665721 - 2² = 77665717 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (77665727) 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, 5547545 + ... + 5547558.

It is an arithmetic number, because the mean of its divisors is an integer number (22190208).

Almost surely, 2^77665721 is an apocalyptic number.

It is an amenable number.

77665721 is a deficient number, since it is larger than the sum of its proper divisors (11095111).

77665721 is a wasteful number, since it uses less digits than its factorization.

77665721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 11095110.

The product of its digits is 123480, while the sum is 41.

The square root of 77665721 is about 8812.8157248407. The cubic root of 77665721 is about 426.6546265998.

The spelling of 77665721 in words is "seventy-seven million, six hundred sixty-five thousand, seven hundred twenty-one".