21489821 has 2 divisors, whose sum is σ = 21489822. Its totient is φ = 21489820.

The previous prime is 21489803. The next prime is 21489827. The reversal of 21489821 is 12898412.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 14546596 + 6943225 = 3814^2 + 2635^2 .

It is a cyclic number.

It is not a de Polignac number, because 21489821 - 2¹⁴ = 21473437 is a prime.

It is a super-2 number, since 2×21489821² = 923624813224082, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21489827) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10744910 + 10744911.

It is an arithmetic number, because the mean of its divisors is an integer number (10744911).

Almost surely, 2^21489821 is an apocalyptic number.

It is an amenable number.

21489821 is a deficient number, since it is larger than the sum of its proper divisors (1).

21489821 is an equidigital number, since it uses as much as digits as its factorization.

21489821 is an evil number, because the sum of its binary digits is even.

The product of its digits is 9216, while the sum is 35.

The square root of 21489821 is about 4635.7114880027. The cubic root of 21489821 is about 278.0209988796.

The spelling of 21489821 in words is "twenty-one million, four hundred eighty-nine thousand, eight hundred twenty-one".