670636721 has 4 divisors (see below), whose sum is σ = 670691700. Its totient is φ = 670581744.

The previous prime is 670636709. The next prime is 670636777. The reversal of 670636721 is 127636076.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It can be written as a sum of positive squares in 2 ways, for example, as 394578496 + 276058225 = 19864^2 + 16615^2 .

It is a cyclic number.

It is not a de Polignac number, because 670636721 - 2¹⁸ = 670374577 is a prime.

It is a super-2 number, since 2×670636721² = 899507223107263682, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (670636321) 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 in 3 ways as a sum of consecutive naturals, for example, 86 + ... + 36623.

It is an arithmetic number, because the mean of its divisors is an integer number (167672925).

Almost surely, 2^670636721 is an apocalyptic number.

It is an amenable number.

670636721 is a deficient number, since it is larger than the sum of its proper divisors (54979).

670636721 is a wasteful number, since it uses less digits than its factorization.

670636721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 54978.

The product of its (nonzero) digits is 63504, while the sum is 38.

The square root of 670636721 is about 25896.6546295076. The cubic root of 670636721 is about 875.3111148363.

The spelling of 670636721 in words is "six hundred seventy million, six hundred thirty-six thousand, seven hundred twenty-one".