647568721 has 2 divisors, whose sum is σ = 647568722. Its totient is φ = 647568720.

The previous prime is 647568653. The next prime is 647568737. The reversal of 647568721 is 127865746.

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., 492840000 + 154728721 = 22200^2 + 12439^2 .

It is a cyclic number.

It is not a de Polignac number, because 647568721 - 2¹⁵ = 647535953 is a prime.

It is not a weakly prime, because it can be changed into another prime (647568791) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 323784360 + 323784361.

It is an arithmetic number, because the mean of its divisors is an integer number (323784361).

Almost surely, 2^647568721 is an apocalyptic number.

It is an amenable number.

647568721 is a deficient number, since it is larger than the sum of its proper divisors (1).

647568721 is an equidigital number, since it uses as much as digits as its factorization.

647568721 is an evil number, because the sum of its binary digits is even.

The product of its digits is 564480, while the sum is 46.

The square root of 647568721 is about 25447.3715931528. The cubic root of 647568721 is about 865.1577205802.

The spelling of 647568721 in words is "six hundred forty-seven million, five hundred sixty-eight thousand, seven hundred twenty-one".