5661991 has 2 divisors, whose sum is σ = 5661992. Its totient is φ = 5661990.

The previous prime is 5661973. The next prime is 5662039. The reversal of 5661991 is 1991665.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 5661991 - 2¹¹ = 5659943 is a prime.

It is an Ulam number.

It is a self number, because there is not a number n which added to its sum of digits gives 5661991.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (5661911) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 2830995 + 2830996.

It is an arithmetic number, because the mean of its divisors is an integer number (2830996).

Almost surely, 2^5661991 is an apocalyptic number.

5661991 is a deficient number, since it is larger than the sum of its proper divisors (1).

5661991 is an equidigital number, since it uses as much as digits as its factorization.

5661991 is an evil number, because the sum of its binary digits is even.

The product of its digits is 14580, while the sum is 37.

The square root of 5661991 is about 2379.4938537429. The cubic root of 5661991 is about 178.2336598125.

The spelling of 5661991 in words is "five million, six hundred sixty-one thousand, nine hundred ninety-one".