647723521 has 2 divisors, whose sum is σ = 647723522. Its totient is φ = 647723520.

The previous prime is 647723519. The next prime is 647723561. The reversal of 647723521 is 125327746.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 484880400 + 162843121 = 22020^2 + 12761^2 .

It is a cyclic number.

It is not a de Polignac number, because 647723521 - 2¹ = 647723519 is a prime.

Together with 647723519, it forms a pair of twin primes.

It is not a weakly prime, because it can be changed into another prime (647723561) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 323861760 + 323861761.

It is an arithmetic number, because the mean of its divisors is an integer number (323861761).

Almost surely, 2^647723521 is an apocalyptic number.

It is an amenable number.

647723521 is a deficient number, since it is larger than the sum of its proper divisors (1).

647723521 is an equidigital number, since it uses as much as digits as its factorization.

647723521 is an evil number, because the sum of its binary digits is even.

The product of its digits is 70560, while the sum is 37.

The square root of 647723521 is about 25450.4129828968. The cubic root of 647723521 is about 865.2266531587.

The spelling of 647723521 in words is "six hundred forty-seven million, seven hundred twenty-three thousand, five hundred twenty-one".