669506821 has 2 divisors, whose sum is σ = 669506822. Its totient is φ = 669506820.

The previous prime is 669506791. The next prime is 669506843. The reversal of 669506821 is 128605966.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 506025025 + 163481796 = 22495^2 + 12786^2 .

It is a cyclic number.

It is not a de Polignac number, because 669506821 - 2⁷ = 669506693 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (669506221) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 334753410 + 334753411.

It is an arithmetic number, because the mean of its divisors is an integer number (334753411).

Almost surely, 2^669506821 is an apocalyptic number.

It is an amenable number.

669506821 is a deficient number, since it is larger than the sum of its proper divisors (1).

669506821 is an equidigital number, since it uses as much as digits as its factorization.

669506821 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 155520, while the sum is 43.

The square root of 669506821 is about 25874.8298738369. The cubic root of 669506821 is about 874.8192588861.

The spelling of 669506821 in words is "six hundred sixty-nine million, five hundred six thousand, eight hundred twenty-one".