21542639 has 2 divisors, whose sum is σ = 21542640. Its totient is φ = 21542638.

The previous prime is 21542623. The next prime is 21542663. The reversal of 21542639 is 93624512.

It is a happy number.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21542639 - 2⁴ = 21542623 is a prime.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21547639) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10771319 + 10771320.

It is an arithmetic number, because the mean of its divisors is an integer number (10771320).

Almost surely, 2^21542639 is an apocalyptic number.

21542639 is a deficient number, since it is larger than the sum of its proper divisors (1).

21542639 is an equidigital number, since it uses as much as digits as its factorization.

21542639 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 12960, while the sum is 32.

The square root of 21542639 is about 4641.4048519818. The cubic root of 21542639 is about 278.2485872328.

The spelling of 21542639 in words is "twenty-one million, five hundred forty-two thousand, six hundred thirty-nine".