20778643 has 4 divisors (see below), whose sum is σ = 21088840. Its totient is φ = 20468448.

The previous prime is 20778623. The next prime is 20778673. The reversal of 20778643 is 34687702.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 20778643 - 2²¹ = 18681491 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (20778623) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 154998 + ... + 155131.

It is an arithmetic number, because the mean of its divisors is an integer number (5272210).

Almost surely, 2^20778643 is an apocalyptic number.

20778643 is a deficient number, since it is larger than the sum of its proper divisors (310197).

20778643 is an equidigital number, since it uses as much as digits as its factorization.

20778643 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 310196.

The product of its (nonzero) digits is 56448, while the sum is 37.

The square root of 20778643 is about 4558.3596830439. The cubic root of 20778643 is about 274.9196150726.

The spelling of 20778643 in words is "twenty million, seven hundred seventy-eight thousand, six hundred forty-three".