840447821 has 2 divisors, whose sum is σ = 840447822. Its totient is φ = 840447820.

The previous prime is 840447787. The next prime is 840447823. The reversal of 840447821 is 128744048.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 653824900 + 186622921 = 25570^2 + 13661^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-840447821 is a prime.

Together with 840447823, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (840447823) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 420223910 + 420223911.

It is an arithmetic number, because the mean of its divisors is an integer number (420223911).

Almost surely, 2^840447821 is an apocalyptic number.

It is an amenable number.

840447821 is a deficient number, since it is larger than the sum of its proper divisors (1).

840447821 is an equidigital number, since it uses as much as digits as its factorization.

840447821 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 57344, while the sum is 38.

The square root of 840447821 is about 28990.4781091999. The cubic root of 840447821 is about 943.7064394847.

The spelling of 840447821 in words is "eight hundred forty million, four hundred forty-seven thousand, eight hundred twenty-one".