21777945 has 16 divisors (see below), whose sum is σ = 39822720. Its totient is φ = 9955584.

The previous prime is 21777937. The next prime is 21777947. The reversal of 21777945 is 54977712.

It is not a de Polignac number, because 21777945 - 2³ = 21777937 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21777897 and 21777906.

It is not an unprimeable number, because it can be changed into a prime (21777947) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 103600 + ... + 103809.

It is an arithmetic number, because the mean of its divisors is an integer number (2488920).

Almost surely, 2^21777945 is an apocalyptic number.

It is an amenable number.

21777945 is a deficient number, since it is larger than the sum of its proper divisors (18044775).

21777945 is a wasteful number, since it uses less digits than its factorization.

21777945 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 207424.

The product of its digits is 123480, while the sum is 42.

The square root of 21777945 is about 4666.6845832989. The cubic root of 21777945 is about 279.2580057052.

It can be divided in two parts, 21777 and 945, that added together give a palindrome (22722).

The spelling of 21777945 in words is "twenty-one million, seven hundred seventy-seven thousand, nine hundred forty-five".