668720621 has 2 divisors, whose sum is σ = 668720622. Its totient is φ = 668720620.

The previous prime is 668720603. The next prime is 668720629. The reversal of 668720621 is 126027866.

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., 665072521 + 3648100 = 25789^2 + 1910^2 .

It is a cyclic number.

It is not a de Polignac number, because 668720621 - 2¹⁴ = 668704237 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (668720629) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 334360310 + 334360311.

It is an arithmetic number, because the mean of its divisors is an integer number (334360311).

Almost surely, 2^668720621 is an apocalyptic number.

It is an amenable number.

668720621 is a deficient number, since it is larger than the sum of its proper divisors (1).

668720621 is an equidigital number, since it uses as much as digits as its factorization.

668720621 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 48384, while the sum is 38.

The square root of 668720621 is about 25859.6330407065. The cubic root of 668720621 is about 874.4766921509.

The spelling of 668720621 in words is "six hundred sixty-eight million, seven hundred twenty thousand, six hundred twenty-one".