647549821 has 2 divisors, whose sum is σ = 647549822. Its totient is φ = 647549820.

The previous prime is 647549803. The next prime is 647549827. The reversal of 647549821 is 128945746.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 360620100 + 286929721 = 18990^2 + 16939^2 .

It is a cyclic number.

It is not a de Polignac number, because 647549821 - 2²⁷ = 513332093 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (647549827) 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, 323774910 + 323774911.

It is an arithmetic number, because the mean of its divisors is an integer number (323774911).

Almost surely, 2^647549821 is an apocalyptic number.

It is an amenable number.

647549821 is a deficient number, since it is larger than the sum of its proper divisors (1).

647549821 is an equidigital number, since it uses as much as digits as its factorization.

647549821 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 483840, while the sum is 46.

The square root of 647549821 is about 25447.0002357842. Note that the first 3 decimals coincide. The cubic root of 647549821 is about 865.1493036409.

The spelling of 647549821 in words is "six hundred forty-seven million, five hundred forty-nine thousand, eight hundred twenty-one".