400240021 has 2 divisors, whose sum is σ = 400240022. Its totient is φ = 400240020.

The previous prime is 400240019. The next prime is 400240033. The reversal of 400240021 is 120042004.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 206640625 + 193599396 = 14375^2 + 13914^2 .

It is a cyclic number.

It is not a de Polignac number, because 400240021 - 2¹ = 400240019 is a prime.

Together with 400240019, it forms a pair of twin primes.

It is a junction number, because it is equal to n+sod(n) for n = 400239983 and 400240010.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (400240081) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 200120010 + 200120011.

It is an arithmetic number, because the mean of its divisors is an integer number (200120011).

Almost surely, 2^400240021 is an apocalyptic number.

It is an amenable number.

400240021 is a deficient number, since it is larger than the sum of its proper divisors (1).

400240021 is an equidigital number, since it uses as much as digits as its factorization.

400240021 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 64, while the sum is 13.

The square root of 400240021 is about 20005.9996251125. Note that the first 3 decimals coincide. The cubic root of 400240021 is about 736.9536444145.

Adding to 400240021 its reverse (120042004), we get a palindrome (520282025).

The spelling of 400240021 in words is "four hundred million, two hundred forty thousand, twenty-one".