21977945 has 16 divisors (see below), whose sum is σ = 29443392. Its totient is φ = 15610560.

The previous prime is 21977941. The next prime is 21977953. The reversal of 21977945 is 54977912.

It is not a de Polignac number, because 21977945 - 2² = 21977941 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21977896 and 21977905.

It is not an unprimeable number, because it can be changed into a prime (21977941) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 2282 + ... + 7011.

It is an arithmetic number, because the mean of its divisors is an integer number (1840212).

Almost surely, 2^21977945 is an apocalyptic number.

It is an amenable number.

21977945 is a deficient number, since it is larger than the sum of its proper divisors (7465447).

21977945 is a wasteful number, since it uses less digits than its factorization.

21977945 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 9352.

The product of its digits is 158760, while the sum is 44.

The square root of 21977945 is about 4688.0640993911. The cubic root of 21977945 is about 280.1102669442.

It can be divided in two parts, 21977 and 945, that added together give a palindrome (22922).

The spelling of 21977945 in words is "twenty-one million, nine hundred seventy-seven thousand, nine hundred forty-five".