20640978 has 48 divisors (see below), whose sum is σ = 46904832. Its totient is φ = 6552000.

The previous prime is 20640967. The next prime is 20641001. The reversal of 20640978 is 87904602.

20640978 is a `hidden beast` number, since 2 + 0 + 640 + 9 + 7 + 8 = 666.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 39358 + ... + 39878.

It is an arithmetic number, because the mean of its divisors is an integer number (977184).

Almost surely, 2^20640978 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 20640978, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (23452416).

20640978 is an abundant number, since it is smaller than the sum of its proper divisors (26263854).

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

20640978 is a wasteful number, since it uses less digits than its factorization.

20640978 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 631 (or 628 counting only the distinct ones).

The product of its (nonzero) digits is 24192, while the sum is 36.

The square root of 20640978 is about 4543.2343104885. The cubic root of 20640978 is about 274.3111265053.

The spelling of 20640978 in words is "twenty million, six hundred forty thousand, nine hundred seventy-eight".