20778391 has 2 divisors, whose sum is σ = 20778392. Its totient is φ = 20778390.

The previous prime is 20778389. The next prime is 20778449. The reversal of 20778391 is 19387702.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 20778391 - 2¹ = 20778389 is a prime.

Together with 20778389, it forms a pair of twin primes.

It is a Chen prime.

It is a self number, because there is not a number n which added to its sum of digits gives 20778391.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (20778311) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10389195 + 10389196.

It is an arithmetic number, because the mean of its divisors is an integer number (10389196).

Almost surely, 2^20778391 is an apocalyptic number.

20778391 is a deficient number, since it is larger than the sum of its proper divisors (1).

20778391 is an equidigital number, since it uses as much as digits as its factorization.

20778391 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 21168, while the sum is 37.

The square root of 20778391 is about 4558.3320414380. The cubic root of 20778391 is about 274.9185036746.

The spelling of 20778391 in words is "twenty million, seven hundred seventy-eight thousand, three hundred ninety-one".