3947821 has 4 divisors (see below), whose sum is σ = 3964444. Its totient is φ = 3931200.

The previous prime is 3947809. The next prime is 3947831. The reversal of 3947821 is 1287493.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 1287493 = 239 ⋅5387.

It can be written as a sum of positive squares in 2 ways, for example, as 1010025 + 2937796 = 1005^2 + 1714^2 .

It is a cyclic number.

It is not a de Polignac number, because 3947821 - 2⁷ = 3947693 is a prime.

It is an Ulam number.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (3947831) 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 in 3 ways as a sum of consecutive naturals, for example, 7950 + ... + 8431.

It is an arithmetic number, because the mean of its divisors is an integer number (991111).

Almost surely, 2^3947821 is an apocalyptic number.

It is an amenable number.

3947821 is a deficient number, since it is larger than the sum of its proper divisors (16623).

3947821 is a wasteful number, since it uses less digits than its factorization.

3947821 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 16622.

The product of its digits is 12096, while the sum is 34.

The square root of 3947821 is about 1986.9124288705. The cubic root of 3947821 is about 158.0468402491.

The spelling of 3947821 in words is "three million, nine hundred forty-seven thousand, eight hundred twenty-one".