4021681 has 4 divisors (see below), whose sum is σ = 4025700. Its totient is φ = 4017664.

The previous prime is 4021663. The next prime is 4021727. The reversal of 4021681 is 1861204.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It can be written as a sum of positive squares in 2 ways, for example, as 1461681 + 2560000 = 1209^2 + 1600^2 .

It is a cyclic number.

It is not a de Polignac number, because 4021681 - 2¹⁷ = 3890609 is a prime.

It is a super-2 number, since 2×4021681² = 32347836131522, which contains 22 as substring.

It is a Duffinian number.

4021681 is a lucky number.

It is not an unprimeable number, because it can be changed into a prime (4021601) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 825 + ... + 2953.

It is an arithmetic number, because the mean of its divisors is an integer number (1006425).

Almost surely, 2^4021681 is an apocalyptic number.

It is an amenable number.

4021681 is a deficient number, since it is larger than the sum of its proper divisors (4019).

4021681 is a wasteful number, since it uses less digits than its factorization.

4021681 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4018.

The product of its (nonzero) digits is 384, while the sum is 22.

The square root of 4021681 is about 2005.4129250606. The cubic root of 4021681 is about 159.0263922541.

Adding to 4021681 its reverse (1861204), we get a palindrome (5882885).

The spelling of 4021681 in words is "four million, twenty-one thousand, six hundred eighty-one".