21291945 has 16 divisors (see below), whose sum is σ = 35242560. Its totient is φ = 10963904.

The previous prime is 21291943. The next prime is 21291961. The reversal of 21291945 is 54919212.

It is a cyclic number.

It is not a de Polignac number, because 21291945 - 2¹ = 21291943 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21291943) 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, 24039 + ... + 24908.

It is an arithmetic number, because the mean of its divisors is an integer number (2202660).

Almost surely, 2^21291945 is an apocalyptic number.

It is an amenable number.

21291945 is a deficient number, since it is larger than the sum of its proper divisors (13950615).

21291945 is a wasteful number, since it uses less digits than its factorization.

21291945 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 48984.

The product of its digits is 6480, while the sum is 33.

The square root of 21291945 is about 4614.3195598051. The cubic root of 21291945 is about 277.1650369543.

The spelling of 21291945 in words is "twenty-one million, two hundred ninety-one thousand, nine hundred forty-five".