400020391 has 2 divisors, whose sum is σ = 400020392. Its totient is φ = 400020390.

The previous prime is 400020389. The next prime is 400020407. The reversal of 400020391 is 193020004.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 400020391 - 2¹ = 400020389 is a prime.

Together with 400020389, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (400026391) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 200010195 + 200010196.

It is an arithmetic number, because the mean of its divisors is an integer number (200010196).

Almost surely, 2^400020391 is an apocalyptic number.

400020391 is a deficient number, since it is larger than the sum of its proper divisors (1).

400020391 is an equidigital number, since it uses as much as digits as its factorization.

400020391 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 216, while the sum is 19.

The square root of 400020391 is about 20000.5097685034. The cubic root of 400020391 is about 736.8188196964.

Adding to 400020391 its reverse (193020004), we get a palindrome (593040395).

It can be divided in two parts, 40002039 and 1, that added together give a triangular number (40002040 = T₈₉₄₄).

The spelling of 400020391 in words is "four hundred million, twenty thousand, three hundred ninety-one".