666566261 has 2 divisors, whose sum is σ = 666566262. Its totient is φ = 666566260.

The previous prime is 666566207. The next prime is 666566269. The reversal of 666566261 is 162665666.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 397803025 + 268763236 = 19945^2 + 16394^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-666566261 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (666566269) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 333283130 + 333283131.

It is an arithmetic number, because the mean of its divisors is an integer number (333283131).

Almost surely, 2^666566261 is an apocalyptic number.

It is an amenable number.

666566261 is a deficient number, since it is larger than the sum of its proper divisors (1).

666566261 is an equidigital number, since it uses as much as digits as its factorization.

666566261 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 466560, while the sum is 44.

The square root of 666566261 is about 25817.9445541275. The cubic root of 666566261 is about 873.5366063199.

The spelling of 666566261 in words is "six hundred sixty-six million, five hundred sixty-six thousand, two hundred sixty-one".