666779021 has 2 divisors, whose sum is σ = 666779022. Its totient is φ = 666779020.

The previous prime is 666778979. The next prime is 666779033. The reversal of 666779021 is 120977666.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 493461796 + 173317225 = 22214^2 + 13165^2 .

It is a cyclic number.

It is not a de Polignac number, because 666779021 - 2¹⁰ = 666777997 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (666779041) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 333389510 + 333389511.

It is an arithmetic number, because the mean of its divisors is an integer number (333389511).

Almost surely, 2^666779021 is an apocalyptic number.

It is an amenable number.

666779021 is a deficient number, since it is larger than the sum of its proper divisors (1).

666779021 is an equidigital number, since it uses as much as digits as its factorization.

666779021 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 190512, while the sum is 44.

The square root of 666779021 is about 25822.0646153634. The cubic root of 666779021 is about 873.6295372550.

The spelling of 666779021 in words is "six hundred sixty-six million, seven hundred seventy-nine thousand, twenty-one".