15991321 has 2 divisors, whose sum is σ = 15991322. Its totient is φ = 15991320.

The previous prime is 15991303. The next prime is 15991343. The reversal of 15991321 is 12319951.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 8620096 + 7371225 = 2936^2 + 2715^2 .

It is a cyclic number.

It is not a de Polignac number, because 15991321 - 2⁷ = 15991193 is a prime.

It is not a weakly prime, because it can be changed into another prime (15991021) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 7995660 + 7995661.

It is an arithmetic number, because the mean of its divisors is an integer number (7995661).

Almost surely, 2^15991321 is an apocalyptic number.

It is an amenable number.

15991321 is a deficient number, since it is larger than the sum of its proper divisors (1).

15991321 is an equidigital number, since it uses as much as digits as its factorization.

15991321 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 2430, while the sum is 31.

The square root of 15991321 is about 3998.9149778409. The cubic root of 15991321 is about 251.9386398434.

The spelling of 15991321 in words is "fifteen million, nine hundred ninety-one thousand, three hundred twenty-one".