666220405261 has 2 divisors, whose sum is σ = 666220405262. Its totient is φ = 666220405260.

The previous prime is 666220405241. The next prime is 666220405303. The reversal of 666220405261 is 162504022666.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 488363368900 + 177857036361 = 698830^2 + 421731^2 .

It is a cyclic number.

It is not a de Polignac number, because 666220405261 - 2⁹ = 666220404749 is a prime.

It is a super-2 number, since 2×666220405261² (a number of 24 digits) contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (666220405211) 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, 333110202630 + 333110202631.

It is an arithmetic number, because the mean of its divisors is an integer number (333110202631).

Almost surely, 2^666220405261 is an apocalyptic number.

It is an amenable number.

666220405261 is a deficient number, since it is larger than the sum of its proper divisors (1).

666220405261 is an equidigital number, since it uses as much as digits as its factorization.

666220405261 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 207360, while the sum is 40.

The spelling of 666220405261 in words is "six hundred sixty-six billion, two hundred twenty million, four hundred five thousand, two hundred sixty-one".