20978721 has 12 divisors (see below), whose sum is σ = 30421248. Its totient is φ = 13931064.

The previous prime is 20978719. The next prime is 20978729. The reversal of 20978721 is 12787902.

It is not a de Polignac number, because 20978721 - 2¹ = 20978719 is a prime.

It is not an unprimeable number, because it can be changed into a prime (20978729) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 2065 + ... + 6798.

It is an arithmetic number, because the mean of its divisors is an integer number (2535104).

Almost surely, 2^20978721 is an apocalyptic number.

It is an amenable number.

20978721 is a deficient number, since it is larger than the sum of its proper divisors (9442527).

20978721 is a wasteful number, since it uses less digits than its factorization.

20978721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 9132 (or 9129 counting only the distinct ones).

The product of its (nonzero) digits is 14112, while the sum is 36.

The square root of 20978721 is about 4580.2533772707. The cubic root of 20978721 is about 275.7992001972.

The spelling of 20978721 in words is "twenty million, nine hundred seventy-eight thousand, seven hundred twenty-one".