400021639 has 2 divisors, whose sum is σ = 400021640. Its totient is φ = 400021638.

The previous prime is 400021631. The next prime is 400021663. The reversal of 400021639 is 936120004.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 400021639 - 2³ = 400021631 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (400021631) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 200010819 + 200010820.

It is an arithmetic number, because the mean of its divisors is an integer number (200010820).

Almost surely, 2^400021639 is an apocalyptic number.

400021639 is a deficient number, since it is larger than the sum of its proper divisors (1).

400021639 is an equidigital number, since it uses as much as digits as its factorization.

400021639 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 1296, while the sum is 25.

The square root of 400021639 is about 20000.5409676838. The cubic root of 400021639 is about 736.8195859481.

The spelling of 400021639 in words is "four hundred million, twenty-one thousand, six hundred thirty-nine".