20981521 has 12 divisors (see below), whose sum is σ = 23461200. Its totient is φ = 18744440.

The previous prime is 20981509. The next prime is 20981537. The reversal of 20981521 is 12518902.

It is a de Polignac number, because none of the positive numbers 2^k-20981521 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 20981521.

It is not an unprimeable number, because it can be changed into a prime (20981551) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 5670 + ... + 8608.

It is an arithmetic number, because the mean of its divisors is an integer number (1955100).

Almost surely, 2^20981521 is an apocalyptic number.

It is an amenable number.

20981521 is a deficient number, since it is larger than the sum of its proper divisors (2479679).

20981521 is a wasteful number, since it uses less digits than its factorization.

20981521 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3020 (or 3009 counting only the distinct ones).

The product of its (nonzero) digits is 1440, while the sum is 28.

The square root of 20981521 is about 4580.5590270184. The cubic root of 20981521 is about 275.8114698268.

The spelling of 20981521 in words is "twenty million, nine hundred eighty-one thousand, five hundred twenty-one".