20991285 has 64 divisors (see below), whose sum is σ = 43276800. Its totient is φ = 9455616.

The previous prime is 20991283. The next prime is 20991293. The reversal of 20991285 is 58219902.

It is not a de Polignac number, because 20991285 - 2¹ = 20991283 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20991283) by changing a digit.

It is a polite number, since it can be written in 63 ways as a sum of consecutive naturals, for example, 91551 + ... + 91779.

It is an arithmetic number, because the mean of its divisors is an integer number (676200).

Almost surely, 2^20991285 is an apocalyptic number.

It is an amenable number.

20991285 is an abundant number, since it is smaller than the sum of its proper divisors (22285515).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

20991285 is a wasteful number, since it uses less digits than its factorization.

20991285 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 347 (or 341 counting only the distinct ones).

The product of its (nonzero) digits is 12960, while the sum is 36.

The square root of 20991285 is about 4581.6247118244. The cubic root of 20991285 is about 275.8542472396.

The spelling of 20991285 in words is "twenty million, nine hundred ninety-one thousand, two hundred eighty-five".