15991993 has 2 divisors, whose sum is σ = 15991994. Its totient is φ = 15991992.

The previous prime is 15991961. The next prime is 15992017. The reversal of 15991993 is 39919951.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 10738729 + 5253264 = 3277^2 + 2292^2 .

It is a cyclic number.

It is not a de Polignac number, because 15991993 - 2⁵ = 15991961 is a prime.

It is a super-2 number, since 2×15991993² = 511487680224098, which contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (15991903) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 7995996 + 7995997.

It is an arithmetic number, because the mean of its divisors is an integer number (7995997).

Almost surely, 2^15991993 is an apocalyptic number.

It is an amenable number.

15991993 is a deficient number, since it is larger than the sum of its proper divisors (1).

15991993 is an equidigital number, since it uses as much as digits as its factorization.

15991993 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 98415, while the sum is 46.

The square root of 15991993 is about 3998.9989997498. The cubic root of 15991993 is about 251.9421688492.

The spelling of 15991993 in words is "fifteen million, nine hundred ninety-one thousand, nine hundred ninety-three".