661893391 has 2 divisors, whose sum is σ = 661893392. Its totient is φ = 661893390.

The previous prime is 661893373. The next prime is 661893403. The reversal of 661893391 is 193398166.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 661893391 - 2¹³ = 661885199 is a prime.

It is a super-2 number, since 2×661893391² = 876205722098957762, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (661893301) 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, 330946695 + 330946696.

It is an arithmetic number, because the mean of its divisors is an integer number (330946696).

Almost surely, 2^661893391 is an apocalyptic number.

661893391 is a deficient number, since it is larger than the sum of its proper divisors (1).

661893391 is an equidigital number, since it uses as much as digits as its factorization.

661893391 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 209952, while the sum is 46.

The square root of 661893391 is about 25727.2888388963. The cubic root of 661893391 is about 871.4905487113.

The spelling of 661893391 in words is "six hundred sixty-one million, eight hundred ninety-three thousand, three hundred ninety-one".