21640559 has 2 divisors, whose sum is σ = 21640560. Its totient is φ = 21640558.

The previous prime is 21640547. The next prime is 21640561. The reversal of 21640559 is 95504612.

It is a happy number.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21640559 - 2¹² = 21636463 is a prime.

Together with 21640561, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21640529) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10820279 + 10820280.

It is an arithmetic number, because the mean of its divisors is an integer number (10820280).

Almost surely, 2^21640559 is an apocalyptic number.

21640559 is a deficient number, since it is larger than the sum of its proper divisors (1).

21640559 is an equidigital number, since it uses as much as digits as its factorization.

21640559 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 10800, while the sum is 32.

The square root of 21640559 is about 4651.9414226751. The cubic root of 21640559 is about 278.6695341756.

The spelling of 21640559 in words is "twenty-one million, six hundred forty thousand, five hundred fifty-nine".