28021639 has 2 divisors, whose sum is σ = 28021640. Its totient is φ = 28021638.

The previous prime is 28021633. The next prime is 28021657. The reversal of 28021639 is 93612082.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 28021639 - 2¹⁵ = 27988871 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 28021639.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (28021633) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 14010819 + 14010820.

It is an arithmetic number, because the mean of its divisors is an integer number (14010820).

Almost surely, 2^28021639 is an apocalyptic number.

28021639 is a deficient number, since it is larger than the sum of its proper divisors (1).

28021639 is an equidigital number, since it uses as much as digits as its factorization.

28021639 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 5184, while the sum is 31.

The square root of 28021639 is about 5293.5469205439. The cubic root of 28021639 is about 303.7371017459.

The spelling of 28021639 in words is "twenty-eight million, twenty-one thousand, six hundred thirty-nine".