666400426561 has 2 divisors, whose sum is σ = 666400426562. Its totient is φ = 666400426560.

The previous prime is 666400426507. The next prime is 666400426609. The reversal of 666400426561 is 165624004666.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 581206492161 + 85193934400 = 762369^2 + 291880^2 .

It is a cyclic number.

It is not a de Polignac number, because 666400426561 - 2²¹ = 666398329409 is a prime.

It is not a weakly prime, because it can be changed into another prime (666400426361) 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 as a sum of consecutive naturals, namely, 333200213280 + 333200213281.

It is an arithmetic number, because the mean of its divisors is an integer number (333200213281).

Almost surely, 2^666400426561 is an apocalyptic number.

It is an amenable number.

666400426561 is a deficient number, since it is larger than the sum of its proper divisors (1).

666400426561 is an equidigital number, since it uses as much as digits as its factorization.

666400426561 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 1244160, while the sum is 46.

The spelling of 666400426561 in words is "six hundred sixty-six billion, four hundred million, four hundred twenty-six thousand, five hundred sixty-one".