21605803 has 2 divisors, whose sum is σ = 21605804. Its totient is φ = 21605802.

The previous prime is 21605777. The next prime is 21605807. The reversal of 21605803 is 30850612.

It is a happy number.

It is a strong prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21605803 is a prime.

It is not a weakly prime, because it can be changed into another prime (21605807) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10802901 + 10802902.

It is an arithmetic number, because the mean of its divisors is an integer number (10802902).

Almost surely, 2^21605803 is an apocalyptic number.

21605803 is a deficient number, since it is larger than the sum of its proper divisors (1).

21605803 is an equidigital number, since it uses as much as digits as its factorization.

21605803 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 1440, while the sum is 25.

The square root of 21605803 is about 4648.2042769224. The cubic root of 21605803 is about 278.5202677281.

The spelling of 21605803 in words is "twenty-one million, six hundred five thousand, eight hundred three".