6420991 has 2 divisors, whose sum is σ = 6420992. Its totient is φ = 6420990.

The previous prime is 6420989. The next prime is 6421001. The reversal of 6420991 is 1990246.

It is a happy number.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 6420991 - 2¹ = 6420989 is a prime.

Together with 6420989, it forms a pair of twin primes.

It is a zygodrome in base 2.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (6420901) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 3210495 + 3210496.

It is an arithmetic number, because the mean of its divisors is an integer number (3210496).

Almost surely, 2^6420991 is an apocalyptic number.

6420991 is a deficient number, since it is larger than the sum of its proper divisors (1).

6420991 is an equidigital number, since it uses as much as digits as its factorization.

6420991 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 3888, while the sum is 31.

The square root of 6420991 is about 2533.9674425691. The cubic root of 6420991 is about 185.8663143127.

The spelling of 6420991 in words is "six million, four hundred twenty thousand, nine hundred ninety-one".