647821 has 2 divisors, whose sum is σ = 647822. Its totient is φ = 647820.

The previous prime is 647809. The next prime is 647837. The reversal of 647821 is 128746.

647821 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 532900 + 114921 = 730^2 + 339^2 .

It is a cyclic number.

It is not a de Polignac number, because 647821 - 2⁵ = 647789 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 647821.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (647851) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 323910 + 323911.

It is an arithmetic number, because the mean of its divisors is an integer number (323911).

2⁶⁴⁷⁸²¹ is an apocalyptic number.

It is an amenable number.

647821 is a deficient number, since it is larger than the sum of its proper divisors (1).

647821 is an equidigital number, since it uses as much as digits as its factorization.

647821 is an evil number, because the sum of its binary digits is even.

The product of its digits is 2688, while the sum is 28.

The square root of 647821 is about 804.8732819519. The cubic root of 647821 is about 86.5270055009.

The spelling of 647821 in words is "six hundred forty-seven thousand, eight hundred twenty-one".