3997921 has 2 divisors, whose sum is σ = 3997922. Its totient is φ = 3997920.

The previous prime is 3997919. The next prime is 3997927. The reversal of 3997921 is 1297993.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 3857296 + 140625 = 1964^2 + 375^2 .

It is an emirp because it is prime and its reverse (1297993) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 3997921 - 2¹ = 3997919 is a prime.

Together with 3997919, it forms a pair of twin primes.

3997921 is a lucky number.

It is not a weakly prime, because it can be changed into another prime (3997927) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 1998960 + 1998961.

It is an arithmetic number, because the mean of its divisors is an integer number (1998961).

Almost surely, 2^3997921 is an apocalyptic number.

It is an amenable number.

3997921 is a deficient number, since it is larger than the sum of its proper divisors (1).

3997921 is an equidigital number, since it uses as much as digits as its factorization.

3997921 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 30618, while the sum is 40.

The square root of 3997921 is about 1999.4801824474. The cubic root of 3997921 is about 158.7125987075.

It can be divided in two parts, 39979 and 21, that added together give a square (40000 = 200²).

The spelling of 3997921 in words is "three million, nine hundred ninety-seven thousand, nine hundred twenty-one".