21690481 has 2 divisors, whose sum is σ = 21690482. Its totient is φ = 21690480.

The previous prime is 21690479. The next prime is 21690499. The reversal of 21690481 is 18409612.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 19000881 + 2689600 = 4359^2 + 1640^2 .

It is a cyclic number.

It is not a de Polignac number, because 21690481 - 2¹ = 21690479 is a prime.

It is a super-2 number, since 2×21690481² = 940953932022722, which contains 22 as substring.

Together with 21690479, it forms a pair of twin primes.

It is not a weakly prime, because it can be changed into another prime (21690451) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10845240 + 10845241.

It is an arithmetic number, because the mean of its divisors is an integer number (10845241).

Almost surely, 2^21690481 is an apocalyptic number.

It is an amenable number.

21690481 is a deficient number, since it is larger than the sum of its proper divisors (1).

21690481 is an equidigital number, since it uses as much as digits as its factorization.

21690481 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 3456, while the sum is 31.

The square root of 21690481 is about 4657.3040484813. The cubic root of 21690481 is about 278.8836545939.

The spelling of 21690481 in words is "twenty-one million, six hundred ninety thousand, four hundred eighty-one".