6521661257 has 4 divisors (see below), whose sum is σ = 6522100116. Its totient is φ = 6521222400.

The previous prime is 6521661253. The next prime is 6521661271. The reversal of 6521661257 is 7521661256.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 4175615161 + 2346046096 = 64619^2 + 48436^2 .

It is a cyclic number.

It is not a de Polignac number, because 6521661257 - 2² = 6521661253 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (6521661253) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 196328 + ... + 227129.

It is an arithmetic number, because the mean of its divisors is an integer number (1630525029).

Almost surely, 2^6521661257 is an apocalyptic number.

It is an amenable number.

6521661257 is a deficient number, since it is larger than the sum of its proper divisors (438859).

6521661257 is a wasteful number, since it uses less digits than its factorization.

6521661257 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 438858.

The product of its digits is 151200, while the sum is 41.

The square root of 6521661257 is about 80756.8031623343. The cubic root of 6521661257 is about 1868.3263793688.

Subtracting 6521661257 from its reverse (7521661256), we obtain a palindrome (999999999).

The spelling of 6521661257 in words is "six billion, five hundred twenty-one million, six hundred sixty-one thousand, two hundred fifty-seven".