15981821 has 2 divisors, whose sum is σ = 15981822. Its totient is φ = 15981820.

The previous prime is 15981811. The next prime is 15981827. The reversal of 15981821 is 12818951.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 8637721 + 7344100 = 2939^2 + 2710^2 .

It is a cyclic number.

It is not a de Polignac number, because 15981821 - 2¹⁸ = 15719677 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (15981827) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 7990910 + 7990911.

It is an arithmetic number, because the mean of its divisors is an integer number (7990911).

Almost surely, 2^15981821 is an apocalyptic number.

It is an amenable number.

15981821 is a deficient number, since it is larger than the sum of its proper divisors (1).

15981821 is an equidigital number, since it uses as much as digits as its factorization.

15981821 is an evil number, because the sum of its binary digits is even.

The product of its digits is 5760, while the sum is 35.

The square root of 15981821 is about 3997.7269791720. The cubic root of 15981821 is about 251.8887400427. Note that the first 3 decimals are identical.

The spelling of 15981821 in words is "fifteen million, nine hundred eighty-one thousand, eight hundred twenty-one".