21497689 has 2 divisors, whose sum is σ = 21497690. Its totient is φ = 21497688.

The previous prime is 21497677. The next prime is 21497699. The reversal of 21497689 is 98679412.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 20250000 + 1247689 = 4500^2 + 1117^2 .

It is a cyclic number.

It is not a de Polignac number, because 21497689 - 2⁵ = 21497657 is a prime.

It is not a weakly prime, because it can be changed into another prime (21497669) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10748844 + 10748845.

It is an arithmetic number, because the mean of its divisors is an integer number (10748845).

Almost surely, 2^21497689 is an apocalyptic number.

It is an amenable number.

21497689 is a deficient number, since it is larger than the sum of its proper divisors (1).

21497689 is an equidigital number, since it uses as much as digits as its factorization.

21497689 is an evil number, because the sum of its binary digits is even.

The product of its digits is 217728, while the sum is 46.

The square root of 21497689 is about 4636.5600395121. The cubic root of 21497689 is about 278.0549250550.

It can be divided in two parts, 214 and 97689, that added together give a triangular number (97903 = T₄₄₂).

The spelling of 21497689 in words is "twenty-one million, four hundred ninety-seven thousand, six hundred eighty-nine".