661366681 has 2 divisors, whose sum is σ = 661366682. Its totient is φ = 661366680.

The previous prime is 661366669. The next prime is 661366711. The reversal of 661366681 is 186663166.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 585398025 + 75968656 = 24195^2 + 8716^2 .

It is a cyclic number.

It is not a de Polignac number, because 661366681 - 2⁷ = 661366553 is a prime.

It is a super-2 number, since 2×661366681² = 874811773473911522, which contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (661366481) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 330683340 + 330683341.

It is an arithmetic number, because the mean of its divisors is an integer number (330683341).

Almost surely, 2^661366681 is an apocalyptic number.

It is an amenable number.

661366681 is a deficient number, since it is larger than the sum of its proper divisors (1).

661366681 is an equidigital number, since it uses as much as digits as its factorization.

661366681 is an evil number, because the sum of its binary digits is even.

The product of its digits is 186624, while the sum is 43.

The square root of 661366681 is about 25717.0503946312. The cubic root of 661366681 is about 871.2593208405.

The spelling of 661366681 in words is "six hundred sixty-one million, three hundred sixty-six thousand, six hundred eighty-one".