661378213 has 2 divisors, whose sum is σ = 661378214. Its totient is φ = 661378212.

The previous prime is 661378181. The next prime is 661378229. The reversal of 661378213 is 312873166.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 606292129 + 55086084 = 24623^2 + 7422^2 .

It is a cyclic number.

It is not a de Polignac number, because 661378213 - 2⁵ = 661378181 is a prime.

It is a super-2 number, since 2×661378213² = 874842281262146738, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (661378243) 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, 330689106 + 330689107.

It is an arithmetic number, because the mean of its divisors is an integer number (330689107).

Almost surely, 2^661378213 is an apocalyptic number.

It is an amenable number.

661378213 is a deficient number, since it is larger than the sum of its proper divisors (1).

661378213 is an equidigital number, since it uses as much as digits as its factorization.

661378213 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 36288, while the sum is 37.

The square root of 661378213 is about 25717.2746028812. The cubic root of 661378213 is about 871.2643847506.

The spelling of 661378213 in words is "six hundred sixty-one million, three hundred seventy-eight thousand, two hundred thirteen".