21248639 has 2 divisors, whose sum is σ = 21248640. Its totient is φ = 21248638.

The previous prime is 21248599. The next prime is 21248641. The reversal of 21248639 is 93684212.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21248639 - 2¹⁶ = 21183103 is a prime.

Together with 21248641, it forms a pair of twin primes.

It is a Chen prime.

It is a junction number, because it is equal to n+sod(n) for n = 21248599 and 21248608.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21248659) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10624319 + 10624320.

It is an arithmetic number, because the mean of its divisors is an integer number (10624320).

Almost surely, 2^21248639 is an apocalyptic number.

21248639 is a deficient number, since it is larger than the sum of its proper divisors (1).

21248639 is an equidigital number, since it uses as much as digits as its factorization.

21248639 is an evil number, because the sum of its binary digits is even.

The product of its digits is 20736, while the sum is 35.

The square root of 21248639 is about 4609.6246051061. The cubic root of 21248639 is about 276.9769993978.

The spelling of 21248639 in words is "twenty-one million, two hundred forty-eight thousand, six hundred thirty-nine".