21991945 has 8 divisors (see below), whose sum is σ = 26478144. Its totient is φ = 17535024.

The previous prime is 21991943. The next prime is 21991951. The reversal of 21991945 is 54919912.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21991945 - 2¹ = 21991943 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21991898 and 21991907.

It is not an unprimeable number, because it can be changed into a prime (21991943) 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 7 ways as a sum of consecutive naturals, for example, 5629 + ... + 8698.

It is an arithmetic number, because the mean of its divisors is an integer number (3309768).

Almost surely, 2^21991945 is an apocalyptic number.

It is an amenable number.

21991945 is a deficient number, since it is larger than the sum of its proper divisors (4486199).

21991945 is a wasteful number, since it uses less digits than its factorization.

21991945 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 14639.

The product of its digits is 29160, while the sum is 40.

The square root of 21991945 is about 4689.5570153267. The cubic root of 21991945 is about 280.1697312746.

The spelling of 21991945 in words is "twenty-one million, nine hundred ninety-one thousand, nine hundred forty-five".