7921981 has 2 divisors, whose sum is σ = 7921982. Its totient is φ = 7921980.

The previous prime is 7921943. The next prime is 7921987. The reversal of 7921981 is 1891297.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 5062500 + 2859481 = 2250^2 + 1691^2 .

It is an emirp because it is prime and its reverse (1891297) is a distict prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-7921981 is a prime.

It is a super-2 number, since 2×7921981² = 125515565928722, which contains 22 as substring.

It is a self number, because there is not a number n which added to its sum of digits gives 7921981.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (7921987) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 3960990 + 3960991.

It is an arithmetic number, because the mean of its divisors is an integer number (3960991).

Almost surely, 2^7921981 is an apocalyptic number.

It is an amenable number.

7921981 is a deficient number, since it is larger than the sum of its proper divisors (1).

7921981 is an equidigital number, since it uses as much as digits as its factorization.

7921981 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 9072, while the sum is 37.

The square root of 7921981 is about 2814.6013927375. The cubic root of 7921981 is about 199.3477166113.

The spelling of 7921981 in words is "seven million, nine hundred twenty-one thousand, nine hundred eighty-one".