661931 has 2 divisors, whose sum is σ = 661932. Its totient is φ = 661930.

The previous prime is 661909. The next prime is 661939. The reversal of 661931 is 139166.

661931 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 661931 - 2¹⁸ = 399787 is a prime.

It is a super-2 number, since 2×661931² = 876305297522, which contains 22 as substring.

It is a Chen prime.

It is a self number, because there is not a number n which added to its sum of digits gives 661931.

It is not a weakly prime, because it can be changed into another prime (661939) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 330965 + 330966.

It is an arithmetic number, because the mean of its divisors is an integer number (330966).

2⁶⁶¹⁹³¹ is an apocalyptic number.

661931 is a deficient number, since it is larger than the sum of its proper divisors (1).

661931 is an equidigital number, since it uses as much as digits as its factorization.

661931 is an evil number, because the sum of its binary digits is even.

The product of its digits is 972, while the sum is 26.

The square root of 661931 is about 813.5914208004. The cubic root of 661931 is about 87.1507054525.

The spelling of 661931 in words is "six hundred sixty-one thousand, nine hundred thirty-one".