647387821 has 2 divisors, whose sum is σ = 647387822. Its totient is φ = 647387820.

The previous prime is 647387803. The next prime is 647387891. The reversal of 647387821 is 128783746.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 580328100 + 67059721 = 24090^2 + 8189^2 .

It is a cyclic number.

It is not a de Polignac number, because 647387821 - 2⁵ = 647387789 is a prime.

It is a super-2 number, since 2×647387821² = 838221981558256082, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (647387801) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 323693910 + 323693911.

It is an arithmetic number, because the mean of its divisors is an integer number (323693911).

Almost surely, 2^647387821 is an apocalyptic number.

It is an amenable number.

647387821 is a deficient number, since it is larger than the sum of its proper divisors (1).

647387821 is an equidigital number, since it uses as much as digits as its factorization.

647387821 is an evil number, because the sum of its binary digits is even.

The product of its digits is 451584, while the sum is 46.

The square root of 647387821 is about 25443.8169502927. The cubic root of 647387821 is about 865.0771517271.

The spelling of 647387821 in words is "six hundred forty-seven million, three hundred eighty-seven thousand, eight hundred twenty-one".