21493639 has 2 divisors, whose sum is σ = 21493640. Its totient is φ = 21493638.

The previous prime is 21493621. The next prime is 21493643. The reversal of 21493639 is 93639412.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21493639 - 2⁹ = 21493127 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21493598 and 21493607.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21493649) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10746819 + 10746820.

It is an arithmetic number, because the mean of its divisors is an integer number (10746820).

Almost surely, 2^21493639 is an apocalyptic number.

21493639 is a deficient number, since it is larger than the sum of its proper divisors (1).

21493639 is an equidigital number, since it uses as much as digits as its factorization.

21493639 is an evil number, because the sum of its binary digits is even.

The product of its digits is 34992, while the sum is 37.

The square root of 21493639 is about 4636.1232727355. The cubic root of 21493639 is about 278.0374628188.

The spelling of 21493639 in words is "twenty-one million, four hundred ninety-three thousand, six hundred thirty-nine".