21777777 has 12 divisors (see below), whose sum is σ = 35950720. Its totient is φ = 12444408.

The previous prime is 21777773. The next prime is 21777797. The reversal of 21777777 is 77777712.

It is not a de Polignac number, because 21777777 - 2² = 21777773 is a prime.

It is a Duffinian number.

21777777 is a modest number, since divided by 7777 gives 2177 as remainder.

It is not an unprimeable number, because it can be changed into a prime (21777773) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 172777 + ... + 172902.

Almost surely, 2^21777777 is an apocalyptic number.

It is an amenable number.

21777777 is a deficient number, since it is larger than the sum of its proper divisors (14172943).

21777777 is a wasteful number, since it uses less digits than its factorization.

21777777 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 345692 (or 345689 counting only the distinct ones).

The product of its digits is 235298, while the sum is 45.

The square root of 21777777 is about 4666.6665833333. Note that the first 3 decimals coincide. The cubic root of 21777777 is about 279.2572876168.

The spelling of 21777777 in words is "twenty-one million, seven hundred seventy-seven thousand, seven hundred seventy-seven".