61665991 has 2 divisors, whose sum is σ = 61665992. Its totient is φ = 61665990.

The previous prime is 61665979. The next prime is 61666019. The reversal of 61665991 is 19956616.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 61665991 - 2⁵ = 61665959 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (61665941) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 30832995 + 30832996.

It is an arithmetic number, because the mean of its divisors is an integer number (30832996).

Almost surely, 2^61665991 is an apocalyptic number.

61665991 is a deficient number, since it is larger than the sum of its proper divisors (1).

61665991 is an equidigital number, since it uses as much as digits as its factorization.

61665991 is an evil number, because the sum of its binary digits is even.

The product of its digits is 87480, while the sum is 43.

The square root of 61665991 is about 7852.7696387962. The cubic root of 61665991 is about 395.0771435079.

The spelling of 61665991 in words is "sixty-one million, six hundred sixty-five thousand, nine hundred ninety-one".