3994157821 has 2 divisors, whose sum is σ = 3994157822. Its totient is φ = 3994157820.

The previous prime is 3994157819. The next prime is 3994157833. The reversal of 3994157821 is 1287514993.

It is a happy number.

3994157821 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 3677816025 + 316341796 = 60645^2 + 17786^2 .

It is a cyclic number.

It is not a de Polignac number, because 3994157821 - 2¹ = 3994157819 is a prime.

Together with 3994157819, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (3994157801) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 1997078910 + 1997078911.

It is an arithmetic number, because the mean of its divisors is an integer number (1997078911).

Almost surely, 2^3994157821 is an apocalyptic number.

It is an amenable number.

3994157821 is a deficient number, since it is larger than the sum of its proper divisors (1).

3994157821 is an equidigital number, since it uses as much as digits as its factorization.

3994157821 is an evil number, because the sum of its binary digits is even.

The product of its digits is 544320, while the sum is 49.

The square root of 3994157821 is about 63199.3498463394. The cubic root of 3994157821 is about 1586.6278519907.

The spelling of 3994157821 in words is "three billion, nine hundred ninety-four million, one hundred fifty-seven thousand, eight hundred twenty-one".