20979981 has 24 divisors (see below), whose sum is σ = 33523776. Its totient is φ = 12536640.

The previous prime is 20979961. The next prime is 20979983. The reversal of 20979981 is 18997902.

It is not a de Polignac number, because 20979981 - 2⁵ = 20979949 is a prime.

It is a super-2 number, since 2×20979981² = 880319205520722, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20979983) 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 23 ways as a sum of consecutive naturals, for example, 5776 + ... + 8678.

It is an arithmetic number, because the mean of its divisors is an integer number (1396824).

Almost surely, 2^20979981 is an apocalyptic number.

It is an amenable number.

20979981 is a deficient number, since it is larger than the sum of its proper divisors (12543795).

20979981 is a wasteful number, since it uses less digits than its factorization.

20979981 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2993 (or 2990 counting only the distinct ones).

The product of its (nonzero) digits is 81648, while the sum is 45.

The square root of 20979981 is about 4580.3909221812. The cubic root of 20979981 is about 275.8047216656.

The spelling of 20979981 in words is "twenty million, nine hundred seventy-nine thousand, nine hundred eighty-one".