20997985 has 8 divisors (see below), whose sum is σ = 25290216. Its totient is φ = 16736640.

The previous prime is 20997973. The next prime is 20997989. The reversal of 20997985 is 58979902.

It can be written as a sum of positive squares in 4 ways, for example, as 603729 + 20394256 = 777^2 + 4516^2 .

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

It is not a de Polignac number, because 20997985 - 2¹⁷ = 20866913 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (20997989) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 6196 + ... + 8965.

It is an arithmetic number, because the mean of its divisors is an integer number (3161277).

Almost surely, 2^20997985 is an apocalyptic number.

It is an amenable number.

20997985 is a deficient number, since it is larger than the sum of its proper divisors (4292231).

20997985 is a wasteful number, since it uses less digits than its factorization.

20997985 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 15443.

The product of its (nonzero) digits is 408240, while the sum is 49.

The square root of 20997985 is about 4582.3558351573. The cubic root of 20997985 is about 275.8835931777.

The spelling of 20997985 in words is "twenty million, nine hundred ninety-seven thousand, nine hundred eighty-five".