20979781 has 8 divisors (see below), whose sum is σ = 22255200. Its totient is φ = 19721520.

The previous prime is 20979779. The next prime is 20979799. The reversal of 20979781 is 18797902.

It is a happy number.

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

It is a cyclic number.

It is not a de Polignac number, because 20979781 - 2¹ = 20979779 is a prime.

It is a super-2 number, since 2×20979781² = 880302421615922, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20971781) 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, 1726 + ... + 6703.

It is an arithmetic number, because the mean of its divisors is an integer number (2781900).

Almost surely, 2^20979781 is an apocalyptic number.

It is an amenable number.

20979781 is a deficient number, since it is larger than the sum of its proper divisors (1275419).

20979781 is a wasteful number, since it uses less digits than its factorization.

20979781 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 8579.

The product of its (nonzero) digits is 63504, while the sum is 43.

The square root of 20979781 is about 4580.3690899315. The cubic root of 20979781 is about 275.8038452568.

The spelling of 20979781 in words is "twenty million, nine hundred seventy-nine thousand, seven hundred eighty-one".